Your 'popuplog.os2' confirmed that the problem does lie in the WPS process but little else. The fact that the problem is now intermittent leaves me less certain than I was before as to its cause. Given that, I'd like to eliminate the most likely suspects first. Based on the results, we can either start reenabling stuff until it goes bad again or just eliminate more things and hope that dumb luck is on our side.
The first things to go are: your Startup folder, FAT32, and all of XWP (my initial suspicion was that some widget on the XCenter was the culprit).
For the first two, open config.sys. Locate "SET RESTARTOBJECTS=STARTUPFOLDERSONLY,REBOOTONLY" and 'rem' it out, then add "SET RESTARTOBJECTS=NO". Next, find "IFS=C:\OS2\BOOT\fat32.ifs" and "call=C:\OS2\cachef32.exe" and 'rem' them out. (Note that both lines have additional parameters that I've left out to make this easier to read.) Save and close config.sys.
For XWP, we'll use brute force: rename 'C:\sys\apps\xwps' to, say, 'C:\sys\apps\xwps-hide'.
Now reboot and see what happens. If we're lucky and the system is stable, play with it for a few minutes. Be aware that your internet connection may not work, and if you've set any folders to use Xview, they won't open by dbl-clicking - you'll have to use their "Open as" menu (I have to fix that...). Since these crashes are intermittent, you may want to shut down and restart to confirm the problem has been eliminated.
Lets be optimistic and assume this worked, so the next step is reenabling things. First open your Startup folder (in the desktop Computer folder). Dbl-click on each icon and see what happens. No problem? Next, we'll reenable XWP but leave the XCenter plugins disabled. Remove the '-hide' from the xwps folder, then drill down to its plugins directory and rename 'C:\sys\apps\xwps\plugins\xcenter' to 'C:\sys\apps\xwps\plugins\xcenter-hide'. Finally, open config.sys and restore the "SET RESTARTOBJECTS=" line (but not the FAT32 stuff), then reboot.
Still OK? If so, you should have XCenter at the bottom of the screen but it will be missing the window list and time widgets. Now for the big test! Right-click on XCenter and select "Close" from it menu. Next, remove the '-hide' from 'C:\sys\apps\xwps\plugins\xcenter-hide'. Finally, open 'Programs->Utilities'. Therein you'll find an XCenter icon - dbl-click on it and hope for the best. If the system blows up, the culprit is an XCenter widget. If not, it's FAT32. If it seems to be FAT32, feel free to reenable it in config.sys to confirm the diagnosis.
Of course, if you never get this far, we'll just have to keep trying. In that case, posting your config.sys will make it easier to identify what needs to be done next.
Good luck!