I get ZLIB Errors after dovecot upgrade from 2.3.10.1 to 2.3.11.3

Thunderbird reports some error when try to save/open a bigger attachment.

Aug 21 15:27:34 lxc-imap dovecot: imap(acsida)<63870>: Error: Mailbox Sent: UID=40826: read(zlib(/home/vmail/virtualmailboxes/acsida/storage/m.2409)) failed: read(/home/vmail/virtualmailboxes/acsida/storage/m.2409) failed: Broken pipe (FETCH BODY[]) Aug 21 15:27:34 lxc-imap dovecot: imap(acsida)<63871><9A0...>: Error: Mailbox Sent: UID=40826: read(zlib(/home/vmail/virtualmailboxes/acsida/storage/m.2409)) failed: read(/home/vmail/virtualmailboxes/acsida/storage/m.2409) failed: Broken pipe (FETCH BODY[]) Aug 21 15:30:11 lxc-imap dovecot: imap(cpotzinger)<63889>: Error: Mailbox Sent: UID=29495: read(zlib(/home/vmail/virtualmailboxes/cpotzinger/storage/m.4703)) failed: read(/home/vmail/virtualmailboxes/cpotzinger/storage/m.4703) failed: Broken pipe (FETCH BODY[]) Aug 21 15:30:17 lxc-imap dovecot: imap(cpotzinger)<64169>: Error: Mailbox Sent: UID=29495: read(zlib(/home/vmail/virtualmailboxes/cpotzinger/storage/m.4703)) failed: read(/home/vmail/virtualmailboxes/cpotzinger/storage/m.4703) failed: Broken pipe (FETCH BODY[]) Aug

anything I can tweak or do ?

Robert