Maybe I know. PSpad increases size of toobar icons in case he found a higher resolution or DPI. In this case instead of stadard 16x16 icons 24x24 are used. In your case you have Silk toolbar what isn't available in higher resolutions. This change will be aplied when PSpad detects different monitor next time.
If you change it and save it, PSpad should keep it. Please check [x]Don't change toolbar icon size when DPI is changed under settings of tollbar icons. I will check why is it done for Sild, when Silk isn't available in bigger sizes. -- <https://forum.pspad.com/read.php?2,73553,73555> PSPad freeware editor https://www.pspad.com