ntozier Tried by manual, again, no luck.
For what it's worth, I noticed that when I install the plugin in v1.11 (and it immediately goes "defunct-missing"), it does create an entry in the ostum_plugins table, but there are no corresponding rows with namespace=id in the ostum_config table. Dunno if that's diagnostically useful, but I'm out of literally all other ideas, especially considering it appears that no one else is having this issue.