Mail received but not indexed?

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