VTE (libvte-2.91-0) recently received lots of changes to its drawing component. There were bugfixes around rendering, especially in non-compositing mode [1] and many simplifications and cleanups [2] released in version 0.56; followed by even more simplifications and cleanups [3] for version 0.58.
I'm pretty certain that 0.58, if not 0.56 already, fixes the issue. [1] https://gitlab.gnome.org/GNOME/vte/issues/4 [2] https://gitlab.gnome.org/GNOME/vte/issues/26 [3] https://gitlab.gnome.org/GNOME/vte/issues/56 e.