[BUG] Save causes "Sequence contains more than one matching element"

[6TELOIV]

Bug Affects...

[x] edit experience / UI
[x] admin experience UI
[x] Content Types or data management
[x] Platform parts (Dnn/Oqtane)
[x] other / unknown

Current Behavior / Expected Behavior

Occasionally (rarely), users will get a 400 error when saving, with the message "Sequence contains more than one matching element". Once the issue occurs, that specific content item is "corrupt" and will ALWAYS give the same error, regardless of user nor system restarts. The only workaround is deleting and recreating the item from scratch.

To Reproduce (Steps, Videos, Screenshots, Apps)

Unsure how to reproduce; this seems to be a data race issue, where somehow under laggy conditions, multiple entries for the same EntityId are added to the database? I've attached the log for our specific instance of the error, which only really gives insight into the situation once the issue has occured, not how it got that way. It may be near impossible to identify when the issue begins, as there is nothing wrong until the editor tries to save the item again once the corruption has occured; no error occurs when the corruption/duplication happens

Your environment

• 2sxc version(s): 17.09.00
• Browser: all
• DNN / Oqtane: DNN 19.13.02
• Hosting platform: all
• Ui Languages: any/all

Additional context

Log: Sequence contains more than one matching element.htm.txt
Previous probably related issue: #3436
Line causing the overall error: DbEntity_read.cs#L89

[6TELOIV]

My analysis above may be incorrect, based on the line that is causing the error:

dbEntityList
  .GroupBy(e => e.EntityGuid)
  .ToDictionary(
      g => g.Key,
      g => g.Single(e => !e.PublishedEntityId.HasValue).EntityId //This line is finding multiple instead of Single
  );

It may be a data race where 2 "published" entities are created due to multiple saves going through???

Again, not sure what the originating CAUSE is, just the fact that something goes wrong, and then the content item becomes un-saveable.

[iJungleboy]

Possibly related to #3561 - nope, not likely.

[iJungleboy]

actually I think it's probably not related.

The 3561 is a very recent bug.

How often does this happen - every month, every 3 months, every day?

[6TELOIV]

This is the first time it's happened and I've investigated, and we've had 2sxc for about 9 months. At our rate of editing and the amount of content items we'd have, I'd estimate this bug occurs on a magnitude of 1 in 10,000 to 100,000 edits.

I'll post back here if it happens again.