Hi Ridwan;
FYI: Webforms is EOL'ed and was removed from PB in v12.5.2.
FWIW: The Webform feature was always troublesome depending on the features you used and I personally encountered many stability issues like you just posted.
Personally, I would not waste your time on Webforms and instead have a serious look at Appeon Web for PowerBuilder ...
HTH
Regards .. Chris