The stamp tool has a caching problem in Krita 3.3 and the latest release that is the paid version for windows 3.4. Once a stamp is created a new one can not be made at all.
Can confirm in 4.0 beta 1. It just doesn't update the preview for some reason...
I have been able to trick the system to do make a stamp if I switch over to a smear brush. save the stamp. switch back to a regular brush and change the stamp. sometimes that works.
*** Bug 345080 has been marked as a duplicate of this bug. ***
Git commit 429dd9cdadae931b3ce0f37883316d58fad94178 by Ivan Yossi. Committed on 14/06/2019 at 17:53. Pushed by ivany into branch 'master'. Update brush preview on every stamp creation M +2 -0 plugins/paintops/libpaintop/kis_brush_chooser.cpp M +6 -0 plugins/paintops/libpaintop/kis_custom_brush_widget.cpp M +2 -0 plugins/paintops/libpaintop/kis_custom_brush_widget.h https://invent.kde.org/kde/krita/commit/429dd9cdadae931b3ce0f37883316d58fad94178
Git commit ca7ba8d77a8107f1cf39030f9cf0839863e2904b by Boudewijn Rempt, on behalf of Ivan Yossi. Committed on 17/06/2019 at 08:17. Pushed by rempt into branch 'krita/4.2'. Update brush preview on every stamp creation M +2 -0 plugins/paintops/libpaintop/kis_brush_chooser.cpp M +6 -0 plugins/paintops/libpaintop/kis_custom_brush_widget.cpp M +2 -0 plugins/paintops/libpaintop/kis_custom_brush_widget.h https://invent.kde.org/kde/krita/commit/ca7ba8d77a8107f1cf39030f9cf0839863e2904b