The symptoms that both of us are having are that after a certain period of time after playing the game just kind of hangs and stops responding to any further inputs or sending game updates. There is a little bit of animation still going and the last active sounds/music keep going in a normal way, so it's not like there's a complete freeze/hang of the client. I'm almost wondering if it's network related but I am on a wired ethernet connection so find it a bit unlikely that I'm having unreliability issues there, but will have to look more into this later if you think this is the avenue of further testing that should be taken as opposed to something else.
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Anyway... further information for now about my setup.
i7-3770k - 24 GB RAM
nVidia GTX 760 (4GB version) -- should support up to OpenGL 4.3 features?
OS/Java:
Windows 10 / Ubuntu 20.04 LTS -- this issue happens on both operating systems, both of which are fully up to date
Official Java 64-bit 8 on Windows and fully up to date, and 64-bit OpenJDK JRE 8 build 282-b08 on Ubuntu, also up to date
I have never installed the 32-bit Java JVM on either, just the 64-bit packages
Drivers:
Windows 10 - Latest game ready nVidia drivers are installed for my graphics card directly from nVidia website
Ubuntu - have been running latest available nVidia drivers on that as well (as opposed to Mesa)
-- might screw around with this later and try the Mesa drivers, but I have my doubts it's purely graphics driver related??
Command line options I have been running the game with:
javaw -Xms512M -Xmx4G -jar autohaven.jar (Windows 10) -- or even run just by clicking on the jar file, same issue
java -Xms512M -Xmx4G -jar autohaven.jar (Ubuntu)
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Don't think this will be exactly relevant but will post here as well, just in case.
Outputs from :clickdb which I enabled once the movement issue happened
https://imgur.com/a/skyc7r6
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Any help with further troubleshooting steps or solutions would be great. I didn't see any console commands listed that could help with debugging network issues, if that is indeed the case, and I looked via forum search and didn't find anything exactly like this that had been solved, but maybe I was searching for the wrong things? Trying to get this resolved before the start of next world.

Edit: I have also noticed this seems to happen the most often, but not exclusively as far as I remember, when the game loses focus and I tab back in. When that happens, that seems to be the most likely time for this issue to manifest itself. I am wondering if it has something to do with stuff getting out of whack with the game ticks and processing when the game isn't focused that causes it to happen more frequently.