New crash most likely related to Virtual plugin again:

Apr 26 07:40:40 spectre dovecot: imap(tlx@leuxner.net): Panic: file mail-storage.c: line 1836 (mailbox_transaction_begin): assertion failed: (box->opened) Apr 26 07:40:40 spectre dovecot: imap(tlx@leuxner.net): Error: Raw backtrace: /usr/lib/dovecot/libdovecot.so.0(+0x6bc0f) [0x7fdfce48ac0f] -> /usr/lib/dovecot/libdovecot.so.0(+0x6bc6e) [0x7fdfce48ac6e] -> /usr/lib/dovecot/libdovecot.so.0(i_fatal+0) [0x7fdfce4442ce] -> /usr/lib/dovecot/libdovecot-storage.so.0(+0x82299) [0x7fdfce777299] -> /usr/lib/dovecot/modules/lib20_virtual_plugin.so(+0x9f1b) [0x7fdfccc2df1b] -> /usr/lib/dovecot/modules/lib20_virtual_plugin.so(virtual_storage_sync_init+0x564) [0x7fdfccc2eb84] -> /usr/lib/dovecot/libdovecot-storage.so.0(mailbox_sync_init+0x33) [0x7fdfce776e53] -> /usr/lib/dovecot/libdovecot-storage.so.0(mailbox_sync+0x27) [0x7fdfce776f77] -> dovecot/imap tlx@leuxner.net 95.223.79.50 EXAMINE [0x412c13] -> dovecot/imap tlx@leuxner.net 95.223.79.50 EXAMINE [0x41839c] -> dovecot/imap tlx@leuxner.net 95.223.79.50 EXAMINE [0x417400] -> dovecot/imap tlx@leuxner.net 95.223.79.50 EXAMINE [0x4174ba] -> dovecot/imap tlx@leuxner.net 95.223.79.50 EXAMINE [0x417775] -> dovecot/imap tlx@leuxner.net 95.223.79.50 EXAMINE [0x417b22] -> /usr/lib/dovecot/libdovecot.so.0(io_loop_call_io+0x4e) [0x7fdfce49b9fe] -> /usr/lib/dovecot/libdovecot.so.0(io_loop_handler_run_internal+0xd7) [0x7fdfce49c9f7] -> /usr/lib/dovecot/libdovecot.so.0(io_loop_handler_run+0x9) [0x7fdfce49ba89] -> /usr/lib/dovecot/libdovecot.so.0(io_loop_run+0x38) [0x7fdfce49bb08] -> /usr/lib/dovecot/libdovecot.so.0(master_service_run+0x13) [0x7fdfce449673] -> dovecot/imap tlx@leuxner.net 95.223.79.50 EXAMINE [0x40c128] -> /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xfd) [0x7fdfce0b2ead] -> dovecot/imap tlx@leuxner.net 95.223.79.50 EXAMINE [0x40c28d] Apr 26 07:40:40 spectre dovecot: imap(tlx@leuxner.net): Fatal: master: service(imap): child 31334 killed with signal 6 (core not dumped)

Disabling virtual prevents Dovecot from crashing.