I'm using MacBook Pro,mid2015, 15inch, and the system version is 10.14.6; BTT version is 3.202.
I'm finding that Safari is easy to crash when I try to use my own gesture, which is taping sequence ⎡1⎤⎡2⎤⎡3⎤⎡4⎤with an act of shortcuts"command+w", to close one of the tags, and this problem seems to start with the last two macOS versions.
It's a bug in Safari in relation to processing programatically generated cmd+w shortcuts. You can workaround it by using the predefined action "Trigger Menubar Menu Item" in BTT instead of sending a shortcut (only for Safari).