It sounds like it might be a corruption problem. Have you tried resetting the program to defaults?
According to Brothersoft.com
the following to do it with PSP v9:
The article also mentions later versions' shift-click start to reset, so this tip might work for 9.
NataliaPetersonReset Paintshop Pro Versions 9 and X (10)
Open the Paintshop Pro software from Corel and click on "File."
Select "Preferences" to open the "Preferences" menu.
Click on "Reset Preferences" and put a check mark beside all the options and click "OK." The Corel preferences will now be restored to their default settings.
You may need to restart PSP.
Another thing that I have never tried is compatibility mode when starting PSP. If you right click the shortcut you use to start PSP chose properties in the context menu, then Compatibility tab.
On my Win 10 computer (Home) I can choose Windows versions way back to Win 95 (3.11 would be fun but hey, 95 is a sentimental journey too). I don't know if it would help, maybe worth a try to go a version back, as Win 10 keeps changing.
Running as administrator might also be an option for you.
I don't have any experience with Large Address Aware or other memory allocation programs, but maybe try disabling it to start the sleuthing with?