Continuous crashing ZFS server

[Willem Jan Withagen]

Hi,

My file server is crashing about every 15 minutes at the moment.
The panic looks like:

Jun  8 11:48:43 zfs kernel: panic: Solaris(panic): zfs: allocating
allocated segment(offset=12922221670400 size=24576)
Jun  8 11:48:43 zfs kernel:
Jun  8 11:48:43 zfs kernel: cpuid = 1
Jun  8 11:48:43 zfs kernel: KDB: stack backtrace:
Jun  8 11:48:43 zfs kernel: #0 0xffffffff80aada57 at kdb_backtrace+0x67
Jun  8 11:48:43 zfs kernel: #1 0xffffffff80a6bb36 at vpanic+0x186
Jun  8 11:48:43 zfs kernel: #2 0xffffffff80a6b9a3 at panic+0x43
Jun  8 11:48:43 zfs kernel: #3 0xffffffff82488192 at vcmn_err+0xc2
Jun  8 11:48:43 zfs kernel: #4 0xffffffff821f73ba at zfs_panic_recover+0x5a
Jun  8 11:48:43 zfs kernel: #5 0xffffffff821dff8f at range_tree_add+0x20f
Jun  8 11:48:43 zfs kernel: #6 0xffffffff821deb06 at metaslab_free_dva+0x276
Jun  8 11:48:43 zfs kernel: #7 0xffffffff821debc1 at metaslab_free+0x91
Jun  8 11:48:43 zfs kernel: #8 0xffffffff8222296a at zio_dva_free+0x1a
Jun  8 11:48:43 zfs kernel: #9 0xffffffff8221f6cc at zio_execute+0xac
Jun  8 11:48:43 zfs kernel: #10 0xffffffff80abe827 at
taskqueue_run_locked+0x127
Jun  8 11:48:43 zfs kernel: #11 0xffffffff80abf9c8 at
taskqueue_thread_loop+0xc8
Jun  8 11:48:43 zfs kernel: #12 0xffffffff80a2f7d5 at fork_exit+0x85
Jun  8 11:48:43 zfs kernel: #13 0xffffffff80ec4abe at fork_trampoline+0xe
Jun  8 11:48:43 zfs kernel: Uptime: 9m7s

Maybe a known bug?
Is there anything I can do about this?
Any debugging needed?

System is running  FreeBSD 11.1-RELEASE-p10

Thanx,
--WjW