Loaded Tables Randomly Stop Loading

I have an extensive environment using gen 1 dataflows in premium workspaces. Sometimes, tables that are loaded in PQ editor randomly just don't load. They disappear from Service and dataflows which use them as linked tables downstream fail with a "key didn't match" error. They do not appear in the linked table tree as viewed in the downstream dataflow.

For all intents and purposes its as if I turned off that table, but if I reopen the dataflow the table still shows loaded. 

I've found two fixes:

1. Open the dataflow, un-load, save, re-open, re-load, re-save.
2. Duplicate the offending table (create a "(2)" versionn of it) and save, at which point the original usually re-appears. i then have to go back in and delete the duplicate.

The problem is that this is very fiddly and requires editing in code that *should* be unchaging, causing a risk of configuration management issues.

My questions are:

1. Why is this happening?
2. How do I prevent this from happening?
3. When it does happen, is there a simpler fix?