pluploader is not able to login until first user login

[EugenMayer]

Running a jira instance locally, with newer jira (8.x works, 9.16.0 does not) i cannot install a plugin via plupload due to

pipx run pluploader --base-url http://jira.lan --user admin --password admin safe-mode disable
[14:00:03] ERROR    An error occured - check your credentials                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                
           ERROR    Expecting value: line 1 column 1 (char 0)  

This keeps on happening until i login with the user once - from this on pluploader will work as expected.

I'am running Jira 9.16 with pluploader You're using 0.8.3 for this.

I can get it running for old and new confluence instances, as well as jira 8.5.19

There is nothing in the jira logs when failing to login in this particular case

[EugenMayer]

Maybe it is related to the fact that after loggin in i see an You've just been upgraded!?