Cyrus 2.5.10 and CentOS 7.3

Hi lists

After update 2.4.17 to 2.5.10 at CentOS 7.3 I've started see  messages in maillog:

...
May 15 10:04:50 server imaps[22927]: mailbox: longlock shared.folder for 1408.2 seconds
May 15 12:52:27server imaps[30558]: mailbox: longlock shared.folder for 1925.0 seconds
...
May 17 13:33:15 server imaps[14670]: IOERROR: bogus filename "/dev/shm/cyrus-imapd/proc//14028.new" in proc_foreach
May 17 13:38:26 server imaps[13973]: IOERROR: bogus filename "/dev/shm/cyrus-imapd/proc//7338.new" in proc_foreach
...

I think it isn't  good especially when happened "longlock mailbox" because users cannot get access to their mboxes. Please help me with investigation the problem. What kind of tests I have to do to repeat effects? What  longlock means?

==cyrys.conf==
START {
   recover       cmd="ctl_cyrusdb -r"
   idled         cmd="idled"
}
SERVICES {
  imap          cmd="imapd -U 10" listen="imap" proto=tcp4 prefork=5
  imaps         cmd="imapd -s -U 10" listen="imaps" proto=tcp4 prefork=10
  pop3          cmd="pop3d" listen="pop3" proto=tcp4 prefork=3
  pop3s         cmd="pop3d -s" listen="pop3s" proto=tcp4 prefork=3
  sieve         cmd="timsieved" listen="sieve" proto=tcp4 prefork=0
  lmtpunix      cmd="lmtpd" listen="/var/lib/imap/socket/lmtp" prefork=1
}
EVENTS {
   checkpoint    cmd="ctl_cyrusdb -c" period=30
   delprune      cmd="cyr_expire -E 3" at=0400
   tlsprune      cmd="tls_prune" at=0400
   deleteprune cmd="cyr_expire -E 4 -D 30" at=0430
  expungeprune cmd="cyr_expire -E 4 -X 30" at=0445
  squatter      cmd="squatter -isv" at=0600
}

==imapd.conf==
admins: cyrus
allowallsubscribe: yes
allowplaintext: yes
allowusermoves: yes
auditlog: yes
commandmintimer: 2
configdirectory: /var/lib/imap
duplicate_db_path: /dev/shm/cyrus-imapd/duplicate_db
lmtp_downcase_rcpt: no
lmtp_over_quota_perm_failure: yes
lmtp_strict_quota: yes
maxlogins_per_host: 60
mboxname_lockpath: /dev/shm/cyrus-imapd/mboxname_lock
postuser: shared
quotawarn: 98
sendmail: /usr/sbin/sendmail
serverinfo: min
sievedir: /var/lib/imap/sieve
statuscache_db_path: /dev/shm/cyrus-imapd/statuscache_db
tls_ciphers: ALL
tls_client_certs: off
tls_server_ca_file: CA.crt
tls_server_cert: server.crt
tls_server_key: server.key
tls_versions:  ssl3 tls1_0 tls1_1 tls1_2
sasl_mech_list: PLAIN LOGIN
sasl_pwcheck_method: saslauthd
partition-default: /data/mail

other options - default

Add info:
CentOS 7.3 is vm at KVM 
30xCPU
50GiB RAM
3TiB Storage (file system -XFS)

Numder of users - 200


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