When you reinstall it would have change the cms_sessions table back to a HEAP/MEMORY type, I suspect this is still the mysql-random-reset problem you had previously (as nobody else is getting random log outs).

I'm managing to stay logged in, just experienced that issue when adding my addons so I believed it to be something else.

Maybe MySQL is crashing or somehow resetting itself under load. Installing an addon will create a lot of rows in the cms_addon_files table, for example.

Logs me out before I actually install the addon, upon selecting it. I relog in and it installs no problem, but maybe. Neither addon creates any tables, both are quite simple. If you cannot reproduce though, happy to leave it be. I can still manage to install them.

I tested again - both via the plus icon next to an already-imported addon, and importing a new addon from compo.sr, with a keep_* parameter in the URL just in case somehow it's a cookie issue, but all worked as expected - the keep_* parameter remained and no log out.