PowerPoint Add-Ins suddenly dissapear

[gweilo]

Hello everyone,

i have a PowerPoint Add-In which works perfectly fine. However, some
user report, that the Add-In disappears suddenly. When they check the
Add-Ins dialog the Add-In is either unloaded or completely removed (it
is a PowerPoint Plugin). Do you have an idea why this problem occurs?
Is it possible that a workstation or office update disables installed
Add-Ins?

Thank you