Hi everyone,
I am having the same issue and already tried what you suggest, but having no results 
In my case, i am trying to connect a Zoho Mail account, and also tried a Gmail one I got but returning the same: “Unexpected error during account creation”. In both cases, I’ve put the email address correctly in my personal data within the profile.
I’ve checked the data/horde that @ChristophWurst says, and it seems that the Gmail account could conect once, as I can read something in it, but never get anything in the platform.
Wed, 09 Dec 2020 23:02:24 +0000
Connection to: imap://imap.gmail.com:993/
Server connection took 0.1048 seconds.
S: * OK Gimap ready for requests from 185.253.155.236 s1mb72010708wrp
C: 1 CAPABILITY
S: * CAPABILITY IMAP4rev1 UNSELECT IDLE NAMESPACE QUOTA ID XLIST CHILDREN X-GM-EXT-1 XYZZY SASL-IR AUTH=XOAUTH2 AUTH=PLAIN AUTH=PLAIN-CLIENTTOKEN AUTH=OAUTHBEARER AUTH=XOAUTH
S: 1 OK Thats all she wrote! s1mb72010708wrp
Command 1 took 0.0285 seconds.
C: 2 AUTHENTICATE PLAIN [INITIAL CLIENT RESPONSE (username: myemailaccount@gmail.com)]
S: * CAPABILITY IMAP4rev1 UNSELECT IDLE NAMESPACE QUOTA ID XLIST CHILDREN X-GM-EXT-1 UIDPLUS COMPRESS=DEFLATE ENABLE MOVE CONDSTORE ESEARCH UTF8=ACCEPT LIST-EXTENDED LIST-STATUS LITERAL- SPECIAL-USE APPENDLIMIT=35651584
S: 2 OK myemailaccount@gmail.com authenticated (Success)
Command 2 took 0.4033 seconds.
horde_smtp.log doesn’t have nothing inside…
By the way, shouldn’t I get errors in the horde_imap.log?? I am quite confused now haha
…In automatic mode it returns: “Request failed with status code 500”.
The screenshots:
Last credentials I put my Zoho address, but I changed it for ****'s just to make the screenshot xD
I hope someone can give me a clue 
Thank you all