Mail received but not indexed?

[Marc Roos]

I have recently that some users are complaining about that they are not 
getting emails. While I see that they are delivered and in the inbox. 
When I do a doveadm force-resync -u xxxx INBOX it resolves the problem. 
I think this is something recent. Where/how should I resolve this issue?

Recent changes
1. did some os updates 2019-08-27
2. provider took away the ssd for index storage (maybe config issue 
having less iops storage?)

CentOS Linux release 7.6.1810 (Core)
dovecot-2.2.36-3.el7.x86_64
mail_location = 
mbox:~/mail:INBOX=/var/spool/mail/%u:CONTROL=~/mail/control:INDEX=/var/d
ovecot2/%u/index:LAYOUT=maildir++


PS during force-resync, I am getting these 
"index/.INBOX/dovecot.index.log was locked for 176 seconds" on some 
users