Nested-nested entries go missing after root owner entry being saved; need help debugging 😓

[mmikkel]

A client is struggling with an issue where entries in a nested Matrix field intermittently disappear as they're editing content.

The setup:

This is a single-site build, with a section called "Trips". Trip entries have a Matrix field "Programs", which uses the Cards view mode and has a single entry type "Program". Nested program entries have a Matrix field called "Program Content Blocks". This field uses the inline-editable blocks view mode.

As per the client, what happens is that sometimes after they edit and save a "Trip" entry, some of the previously saved/published nested entries in the "Program Content Blocks" field in some of the nested "Program" entries, will disappear.

Details are scarce at this point and I'm unable to reproduce, so it's unclear if this is a workflow issue or an actual bug (and if so, what the prerequisite actions/circumstances are to trigger that bug) – so I'm holding off on creating an issue until I feel more confident one way or the other.

But: In investigating a "Trip" entry where this had occurred, I realised the following by comparing revisions and looking at the affected (nested) entries in the database, and I'm looking for some guidance in trying to figure out what actually happened:

• The Trip entry had a nested "Program" entry that had previously been saved and published. This Program entry had X nested entries in its "Program Content Blocks" field.
• At some point, when the client edited and saved the "Trip" entry, the nested Program entry was assigned a new ID, and the "old" nested Program entry was soft-deleted in the elements database table. The timestamp for the "Trip" entry's dateCreated revision and the timestamp for the dateDeleted column for the "old" Program entry are the same, so this definitely happened within the same request. It's my understanding that the canonical ID for nested entries should not change when editing and saving content in a normal way, including applying drafts or similar, so it's unclear to me why the "Program" nested entry somehow became essentially a different entry, when the Trip entry was saved?
• The "new" Program nested entry only has a subset of the existing nested entries in the "Program Content Blocks" field. Almost like a new "Program" nested entry was somehow created and replaced the old one, but for some reason not all of the entries in the "Program Content Blocks" field was duplicated over to the new entry.
• The "missing" nested entries are still in the database, but they now have the "old", soft-deleted "Program" nested entry as their owner instead of the "new", live "Program" entry.

One additional fact:

• The client claims they were the only one working on the entry when this occurred, and there is no evidence to support otherwise (i.e. all the recent revisions for the Trip entry were authored by the same user)

If we believe the client that they did not copy/paste/delete/do anything weird to the original "Program", but simply double-clicked it to edit it in its slideout, and then saved the root owner "Trip" entry, then I'm left with the following questions:

- In what circumstances, if any, will an existing nested entry be assigned a new ID in the elements table as a result of "normal" content editing in the CP; and the old ID being soft-deleted (i.e. it ends up with a timestamp in the dateDeleted column in the elements table)
- If that is a legitimate thing that could happen, what could be the reason for why Craft apparently fails to duplicate all of the existing nested entries in a Matrix field for that nested entry, in that scenario?

Aside from those questions: for further debugging, I'd appreciate any advice or guidance in terms of what I should look for, where I should look, specific questions to ask the client, etc. to try and figure this one out and ideally, reproduce. The client is essentially saying "I saved the trip and some of the content blocks in one of the programs disappeared" 🤷, but as I'm unable to reproduce or even imagine how that could theoretically happen, I'm kinda stumped.

[brandonkelly]

In what circumstances, if any, will an existing nested entry be assigned a new ID in the elements table as a result of "normal" content editing in the CP; and the old ID being soft-deleted (i.e. it ends up with a timestamp in the dateDeleted column in the elements table)

That will happen when applying a draft (whether normal or provisional). Any nested Matrix entries that were initially created for the draft will be duplicated for the canonical owner entry.

I’m not sure what would prevent the doubly-nested entries from being duplicated along with them, though…

[mmikkel]

Thanks for the input, Brandon – I'll discuss further w/ the client and will try to get to the bottom of what's happening (IMO there is a good chance this is a user error/workflow issue, but it's hard to pin down what the circumstances are when it happens).