Nope, there was no triangle issue. just the generic problem message and a failure. The workflow ui processing spinner kept going forever.
By lots of trial and error I figured it out. When exporting and reimporting a workflow it doesn’t preserve the “run by” field which is necessary for oninterval system triggers. The issue was that “run by” wasn’t set.
I’d consider this a bug… I can’t file an official GitHub bug report in the next few days tho so this might slip between the cracks.