@andstatus I didn't have the chance to make an account on another Pleroma instance yet but I did gather some logs. Unfortunately I had to repeat this several times because queue requests leftover from previous attempts at testing (and cross-referencing behaviour with that of a real GNU Social server) kept polluting the log.

I noticed two issues in those past runs, at least one repeats in this batch of logs:
a) AndStatus on OStatus endpoint of Pleroma instance tried to query /api/account/rate_limit_status.json - this fails because https://pl.smuglo.li/api/account/rate_limit_status.json returns the Pleroma Fe UI with empty content part; meanwhile Shitposter.club, a real GS instance, returns a JSON document after auth - thus cc-ing @lain and @kaniini ; this problem pops up in „commands in a queue” view as well
b) it did the same by accessing /api/statuses/show.json?id=X (where X is an ID) - again, Pleroma just serves a webpage

Attached is a zipfile featuring logs of an attempt to send a post with a file attached on AndStatus with data purged beforehand via Apps screen in Android settings - it still seems to have references to my previously setup alt at @takao but it's much easier to read than it was before. Post composition starts in logs/2018-08-24-04-18-41_log.txt

The result is a post with text but no attachments *shrugs*
smugfreshest.zip