Instances not launching/playing

Please confirm the following.

I checked the existing issues for duplicate problems
I have tried resolving the issue using the support portal
I have ensured my Modrinth App installation is up to date

What version of the Modrinth App are you using?

0.21.10

What operating systems are you seeing the problem on?

Windows 11

Describe the bug

When trying to launch any instance, it says "Starting..." and the live log doesnt start. It also opens a task in the Task Manager called "Zulu Platform x64 Architecture", and upon ending that task I get an error in Modrinth that says "RPC error: RPC connection closed while waiting for a response". This also happens for vanilla instances. Minecraft launches and works fine from the official Minecraft Launcher.

I've tried many things such as restarting my PC and the app, reinstalling/repairing the app, clearing the Modrinth cache and my TEMP files and many other things.

And about the version of the Modrinth App I'm using, I am currently using 0.21.10 but it says here that the latest version of the app is 0.21.11. I've tried finding the download for this version but the GitHub only shows 0.21.10 and the installer installs 0.21.10.

Steps to reproduce

Open Modrinth
Click on any instance
Hit play

Expected behavior

I expect the instance to launch and load perfectly as normal.

Additional context

No response

Update, I've completely reinstalled the latest version of the Modrinth App and I removed all related files.

It still doesn't work.

Update, I'm now on Modrinth App version 0.22.0, and I've tried disabling anti-virus and launching as administrator.

It still doesn't work.

The error now reads "rpc connection closed while waiting for response".

That Zulu is the game (its a jvm that shsould be running the game) Uuh it might be starting in a different way then it should? Does any other launch on ur device?

Minecraft from the regular launcher works fine.

I've switched all 4 Java versions to Eclipse Temurin from Adoptium and the same error occurs. The task opened is now called "OpenJDK Platform binary" which is what it used to be called, before this error started appearing.

Yeah u changed the jvm brand

…

________________________________ From: saturn ***@***.***> Sent: Thursday, 22 October 2026 17:46:45 To: modrinth/code ***@***.***> Cc: Ceebug ***@***.***>; Comment ***@***.***> Subject: Re: [modrinth/code] Instances not launching/playing (Issue #8059) [https://avatars.githubusercontent.com/u/235795093?s=20&v=4]ursaamajorr99 left a comment (modrinth/code#8059)<#8059 (comment)> Minecraft from the regular launcher works fine. I've switched all 4 Java versions to Eclipse Temurin from Adoptium and the same error occurs. The task opened is now called "OpenJDK Platform Binary" which is what it used to be called, before this error started appearing. — Reply to this email directly, view it on GitHub<#8059?email_source=notifications&email_token=BJQB4SFLZADWE5E3TTNBA3D5VGUNLA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTMMZTGQ2TSMBZG4ZKM4TFMFZW63VHMNXW23LFNZ2KKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-6334590972>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/BJQB4SB4JXJFB2DLP4IYKB35VGUNLAVCNFSNUABFKJSXA33TNF2G64TZHMZTOOBXGQ2DKOJUHNEXG43VMU5TKOJVGEYDMMRRGIYKC5QC>. You are receiving this because you commented.Message ID: ***@***.***>

on a fresh cashyos install i had this happen. i have 0 java system installed, only used modrinth to manage java versions.

deets

some system info

$ uname -a
Linux cachyox 7.3.0-4-cachyos #1 SMP PREEMPT_DYNAMIC Fri, 23 Oct 2026 15:03:58 +0000 x86_64 GNU/Linux

Modrinth App 0.21.10
Linux Rolling Release

installed via cachyos store (repo)

Installer ::

Java versions are installed and verified via terminal as working and respecting JVM args

$ /home/$USER/.local/share/ModrinthApp/meta/java_versions/zulu21.54.107-ca-jre21.0.13-linux_x64/bin/java --version
openjdk 21.0.13 2026-10-20 LTS
OpenJDK Runtime Environment Zulu21.54+107-CA (build 21.0.13+9-LTS)
OpenJDK 64-Bit Server VM Zulu21.54+107-CA (build 21.0.13+9-LTS, mixed mode, sharing)

I'm glad its not just a me issue...

Okay it randomly starting working again... I literally didn't touch anything for like 3 days.

xD

…

________________________________ From: saturn ***@***.***> Sent: Sunday, 25 October 2026 09:54:43 To: modrinth/code ***@***.***> Cc: Ceebug ***@***.***>; Comment ***@***.***> Subject: Re: [modrinth/code] Instances not launching/playing (Issue #8059) [https://avatars.githubusercontent.com/u/235795093?s=20&v=4]ursaamajorr99 left a comment (modrinth/code#8059)<#8059 (comment)> Okay it randomly starting working again... I literally didn't touch anything for like 3 days. — Reply to this email directly, view it on GitHub<#8059?email_source=notifications&email_token=BJQB4SHMBS6E7HZ6RNI2M635VUXLHA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTMMZZGA2TOMJRGU3KM4TFMFZW63VHMNXW23LFNZ2KKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-6390571156>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/BJQB4SC2O4NMTYYAUKX7D2L5VUXLHAVCNFSNUABFKJSXA33TNF2G64TZHMZTOOBXGQ2DKOJUHNEXG43VMU5TKOJVGEYDMMRRGIYKC5QC>. You are receiving this because you commented.Message ID: ***@***.***>

omfg same. just tested and it works.

im happy to close the issue lol

if you are also on arch or cachyos and it happens to you, ensure prism can work (which is what i did) to play that same day, adn then just go about your business for 36hrs and check in with vulkaninfo and uname -a nad stuff as you do and restart a bunch as you do (because of course you are ricing your linux distro) and it sohuld work next time you start up modrinth ;p

ensure your java works ofc.

I can't imagine modrinth does anything special compared to prism, so if in a terminal you can launch java, just ensure the JVM args, the actual path, is all invocable by your user and the PID modrinth has is good and you should be off to the races again.

i can only assume some kind of file ownership, weird race condition, permissioning thing, or something occurs that requires a restart or two.

Closed becaues it's fixed i guess 😭

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Instances not launching/playing #8059

Please confirm the following.

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Instances not launching/playing #8059

Description

Please confirm the following.

What version of the Modrinth App are you using?

What operating systems are you seeing the problem on?

Describe the bug

Steps to reproduce

Expected behavior

Additional context

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ursaamajorr99 commented on Oct 21, 2026

ursaamajorr99 commented on Oct 22, 2026

ursaamajorr99 commented on Oct 22, 2026

Ceebug commented on Oct 22, 2026

ursaamajorr99 commented on Oct 22, 2026

Ceebug commented on Oct 22, 2026

snewell92 commented on Oct 24, 2026

ursaamajorr99 commented on Oct 24, 2026

ursaamajorr99 commented on Oct 24, 2026

Ceebug commented on Oct 24, 2026

snewell92 commented on Oct 25, 2026

ursaamajorr99 commented on Oct 25, 2026

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