Error handling is one of the weak points of VBA in Visio. People do not realize they might be missing quite a few errors (Visio VBA often doesn't even show you errors that occur because it expects YOU to handle them, and such silent errors can/will cause other issues down the line).
vbWatchDog is an error handling solution that can be used as a global error handler in VBA, although the solution is offered on a Microsoft Access-focused website it works in all Microsoft Office desktop applications (Visio/Word/Excel/Powerpoint).
I am using vbWatchDog in Visio for more than a year now and it has saved me a ton of error handling code, by global error handling almost everything, and I have caught quite a few exceptions that would have gone unnoticed otherwise.
If you are interested check out this link and install the evaluation version:
https://www.everythingaccess.com/vbwatchdog.asp
(this is not a paid promotion, I am not an affiliate of the product maker, I love using the vbWatchDog software AND I believe their TwinBasic solution that is under development is the future of VBA and Visio COM add-ins!)