Auto fech in mailbox integrations fails

I have configured MailBox integration in my standalone youtrack.

Everything goes correct during two months.. but since the other days the autofetch process starts to fail. I can do the fetch process manual, and everything goes correct but the automatic process fails.

Also if I try to change the fetching interval, always return to the old value. I check the logs and detect these two scenarios:

mailbox.log

09 Mar 2018 16:11:39,517 INFO [lboxSettingsListener] [tp1658596529-32]  [Settings] Mailbox cron expression changed to: 0 0/15 * * * ?
09 Mar 2018 16:11:39,517 INFO [lboxSettingsListener] [tp1658596529-32] [Settings] Mailbox cron expression changed to: */15 * * * *
09 Mar 2018 16:12:47,504 INFO [lboxSettingsListener] [tp1658596529-29] [Settings] Mailbox cron expression changed to: 0 0/20 * * * ?
09 Mar 2018 16:12:47,504 INFO [lboxSettingsListener] [tp1658596529-29]  [Settings] Mailbox cron expression changed to: */15 * * * *
09 Mar 2018 16:13:26,615 INFO [lboxSettingsListener] [tp1658596529-29]  Settings] Mailbox cron expression changed to: 0 0/10 * * * ?
09 Mar 2018 16:13:26,615 INFO [lboxSettingsListener] [tp1658596529-29] [Settings] Mailbox cron expression changed to: */15 * * * *

errors.log

09 Mar 2018 16:13:26,615 ERROR [LocalScheduling ] [qtp1658596529-29 ]  job MailboxFetchEmailsScheduling can't be rescheduled!
09 Mar 2018 16:13:26,615 ERROR [EventsMultiplexer ] [qtp1658596529-29 ] Exception while notifying entity listener.
java.text.ParseException: Unexpected end of expression.
at org.quartz.CronExpression.buildExpression(CronExpression.java:494)
at org.quartz.CronExpression.<init>(CronExpression.java:276)
at jetbrains.charisma.scheduling.QuartzParametersFactory.newTrigger(QuartzParametersFactory.kt:21)
at jetbrains.charisma.scheduling.LocalScheduling.reschedule(LocalScheduling.kt:77)
at jetbrains.youtrack.mailbox.persistence.listeners.MailboxSettingsListener.updatedSync(MailboxSettingsListener.kt:28)
at jetbrains.youtrack.mailbox.persistence.listeners.MailboxSettingsListener.updatedSync(MailboxSettings

What should be the problem? I try to restart the youtrack service, recreate the mailbox integration, etc.