Getting "An error occurred; please try again" when flagging on several different sites

Question

Flagging was working properly for me shortly before the recent maintenance occurred, explained in Network-wide maintenance scheduled starting Wednesday, March 26, 2025 from 9:30 am to 12:30 pm ET (13:30 to 16:30 UTC) (but, as indicated in desertnaut's comment, it stopped working sometime earlier on Stats SE). However, since then, when trying to flag, such as want an intuitionistic/constructivist proof of why a number has only finitely many divisors on MathOverflow, using "Needs Improvement | A community-specific reason | This question is not about research level mathematics.", I get an error message of "An error occurred; please try again". Also, the developer console displays that "500 (Internal Server Error)" has occurred, as shown below:

Show error message and browser console

Note that I also get the same error message when trying to flag Is there an API that could parse contextually a given keyword(s)? on Stack Overflow, using "Needs Improvement | A community-specific reason | Seeking recommendations for software libraries, tutorials, tools, books or other off-site resources". The developer console shows basically the same thing as above, except the URL is https://stackoverflow.com/error instead.

These errors occur both when using 64-bit Microsoft Edge, version 134.0.3124.83, on Windows 10, as well as with 64-bit Firefox, version 115.21.0esr, on Windows 7. Also, I have not installed any browser extensions or other such tools, such as Adblocker, with either browser.

• Glorfindel: Reproduced - could be related to today's maintenance, though I don't understand why. The currently deployed build (2025年3月25日.24406) is from yesterday, so a bug in the build would've been noticed earlier.
• John Omielan: @Glorfindel Thanks for your feedback, including confirming you could reproduce the error. Note that I was able to successfully flag on StackOverflow earlier today, shortly before today's maintenance started, but not afterwards (i.e., the 2 attempts above were my first ones). As such, I agree it's likely related to whatever occurred during the maintenance period.
• Francisco IA Lover: At some point I think this type of error was associated with some versions of addblock.
• John Omielan: @FranciscoIALover Thanks for the feedback. However, I'm not using any add-ons with either of the 2 browsers I mentioned, and flagging was working properly with both sites before the maintenance started. Nonetheless, I will update my question to make this explicit.
• user152859: Far fetched, but perhaps related to user permissions which are cached. So try to logout and login again, then flag. (The maintenance was for "experimenting" with server side cache.)
• John Omielan: @ShadowWizzard Thanks for the suggestion. However, I tried logging out and back in a couple of times, but without it making any difference, i.e., I'm still getting those errors.
• desertnaut: @Glorfindel had this issue in Stats SE since yesterday evening (still have), so I don't think it is related to today's maintenance
• Myungheon Lee: It is unresolved, happening again now. I tried log-out and in several times, and I got neumorous error.

Answer 1

This issue should now be resolved.

We introduced this bug while fixing the issue that allowed users to create empty close reasons. We used a method that lacked a null reference check to remove invisible characters from the close reason string. As a result, when flagging without a custom reason — meaning the reason was null — the server threw an error.

• Shiyao Li: Hi @JohnOmielan. This was my mistake. I introduced this bug while fixing the issue that allowed users to create empty close reasons (meta.stackexchange.com/questions/359283/…). I used the wrong method to remove invisible characters from the close reason string, and that method lacked a null reference check. As a result, when flagging without a custom reason—meaning the reason was null—the server threw an error.
• user152859: @ShiyaoLi ah those shiny repz could be yours then. :-D