LHC@home

Change the following line to a high number in global_prefs_override.xml to prevent BOINC from switching between tasks. If the line is not there just add it.:

<cpu_scheduling_period_minutes>10080.000000</cpu_scheduling_period_minutes>

I have mine set to 10080 minutes (1 week). I have the same setting on my Windows and Linux BOINC setups. I don't see a good reason to switch between tasks mid-task, just let a task finish before moving to the next one. For a project like ATLAS and maybe Theory this setting is necessary.

This happens when the BOINC client switches from ATLAS to another task and back.
You may check if "leave non-GPU apps in RAM when paused" from the preferences menu solves the issue.
If not, you may need a separate client that doesn't run any other project.
Even then, stopping the client or a shutdown/reboot will cause ATLAS to start from scratch.

The reason is because you're running it on WSL2. WSL2 is not exactly the same as regular Linux (Ubuntu in your case) because it has a custom kernel and it's init.d, not systemd.

It's good to see others use WSL2 for BOINC projects but it does have its quirks in LHC. One of them is that native ATLAS can only be ran single core in WSL2 and fails when you try to run it multi-core. I've tried to figure out a solution to that a few times in the past but no success so far.

Another quirk is that native Theory doesn't run on WSL2 without a modification (it's an easy one though), which took me a while to figure out. If you're thinking of running Theory check out this post: https://lhcathome.cern.ch/lhcathome/forum_thread.php?id=5777&postid=46031, it should be at the bottom of the thread.

I like WSL2 because you can run Linux projects on Windows machines with minimal resources compared to regular virtual machines. I used to use Hyper-V before learning about WSL2 and now very rarely use Hyper-V.