I am using Zotero 5.0.82 and MS Word 365, and when I click "add/edit citation" in the Zotero plugin in word, instead of getting the usual red outlined box to enter text, a white window flashes open and closed. I followed the procedure above copying and pasting Zotero.dotm as instructed, but this had no effect. The last time I used Zotero with this computer and same software was about 8 weeks ago. Both Zotero and MS Word updates have been installed since then. I turned on Debug Output while clicking on Add/Edit Citation, and nothing happened immediately...but a few minutes later, some lines appeared which I submitted with Debug ID D1722887385. Thank you for any help, I have a report due tomorrow.

I restarted the computer, and clicked add/edit citation, my monitor window flashes white (where the red outlined text box would normally appear), and again submitted debug output D517507837, but it doesn't appear much was logged. Our university IT department started using Avecto Defendpoint recently...this causes Zotero to be run as a "Trusted Application", where a flag appears each time I launch it saying it is a Trusted Application that is "approved and audited". I think what must be happening is that Avecto Defendpoint is blocking the method used to open that window.

That seems likely. I'm afraid that's something you'll need to take up with your IT department.

Update: I have a backup laptop, exact same make and model, with the same software installed. I just tried Zotero on it, and it is working normally, using the same exact document and so forth. So if you want me to compare anything between these two laptops, there is some configuration or setting causing a problem, I'd like to resolve it.

The debug ID you have submitted does not have any word plugin related activity, so either you performed the debug logging procedure wrong, or the white flash that you are seeing isn't actually a Zotero window that fails to open, but rather a Word prompt, or even something from the security software.

Since this is certainly caused by some interaction between your security software (and possibly group permissions) on the computer and isn't a Zotero bug as such and cannot be debugged with any standard procedures, I think we can provide limited troubleshooting ideas. You could try using the Word plugin on the computer with a different user account to see whether account specific configuration may play a role.

Reinstalling Zotero generally does not help with Zotero issues but in this weird case perhaps could not hurt, even if the differing registry key is very unlikely to be the culprit.