Send mail not populating TO

We just updated to 8.8.1.
The new send mail function is not populating the TO field with the affected users mail adress.
In the conole log i get
GET http://tst-sc-sm01/api/V3/Enum/GetEnumDisplayName?id= 500 (Internal Server Error)
When i try to manually select a user i get
(invalid mailadress)

Answers
I'll do my best to try and break this now.
Will try it on Monday!
Also noticed some other strange behaviors, the status is blanked if you dont select a status when sending an email.
Below anser from Cireson sorted both the TO not getting populated and the status being set to "NULL"