Error 3400 - looking for the origin

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Hi there,
it has been discussed a few times here but the reason in still unclear.

It happens to me since I have Plan 2 (at work). Error 3400, Action 1016, Action 2463. While using Visio 2010 or Visio 2016 it doesn't show up.

It happens while copying some shape or closing/saving the file I work with.
It happens not every time I do the action - let's say 25 to 40%. I save the files frequently.
When it happens I do the action again and then it works as expected. I never needed a 3rd try.
The program didn't crash - never (ok, at least until now).

The files I work with doesn't contain any Excel-sheet nor are there some illegal characters in filename or location nor inside the file or shapesheets (which was "identified" in some discussions elsewhere).
The files contain some vba (to assign shapes together or activate layers). No external data handling, nothing sophisticated. Files without vba are not affected so far.

Currently I ignore this (because it works at the 2nd try).

I also asked our "Expats" whose response was reinstalling the program, create the same file again, blabla. It doesn't help.
Maybe it's a good idea to escalate it again and let them mess around with it.

The company update frequently (usually twice a week) the "system" but I don't know what exactly.

These are the facts I experienced.

Is there anything I can do to get the root cause of this or is it just a bug?
The discussions here and elswhere shows that this effect takes place at least a decade ago.

One thing I can imagine to change the filename to .zip and check the content but I'm not experienced with xml nor I have an idea what to look for.

My major concern: if the file gets corrupt due to any reason the degree of corruption may increase and at some point nothing works.

Any ideas?

Thanks!

hl