@FaxLab3D @Shaw @Monz @Katanalevy If you have the time, we would appreciate it if you could confirm whether this issue still occurs for you in 5.3.
In versions prior to 5.3, we had an issue with the UE StylusInput plugin, which is preliminary support for pen-tablets in UE Editor, that only Modeling Mode was enabling (which explains why disabling Modeling Mode fixes it).
The issue only occurred for some users, perhaps users with a tablet connected, or some other specific device (we are not certain as the Windows Ink system we use for Stylus Support also supports mouse and touch input devices, so it may not be strictly related to pen tablets). We disabled the Stylus Plugin dependency in Modeling Mode in 5.3 to work around the issue.
However, a user on Twitter has stated that they are seeing this behavior in 5.3. So, I am hoping one of you can confirm this and/or be willing to DM with me to try to troubleshoot what is happening (because internally we are not sure how to reproduce it)