Trying the first kernel without the change event sauce also fails:

[  532.823594] bcache: run_cache_set() invalidating existing data
[  532.828876] bcache: register_cache() registered cache device nvme0n1p2
[  532.869716] bcache: register_bdev() registered backing device vda1
[  532.994355] bcache: bch_cached_dev_attach() Caching vda1 as bcache0 on set 21d89237-231d-4af6-a4c8-4b1b8fa5eef5
[  533.051588] bcache: register_bcache() error /dev/vda1: device already registered
[  533.094717] bcache: register_bcache() error /dev/vda1: device already registered
[  533.120063] bcache: register_bcache() error /dev/vda1: device already registered
[  533.142517] bcache: register_bcache() error /dev/vda1: device already registered
[  533.191069] bcache: register_bcache() error /dev/vda1: device already registered
[  533.249877] bcache: register_bcache() error /dev/vda1: device already registered
[  533.282653] bcache: register_bcache() error /dev/vda1: device already registered
[  533.301225] bcache: register_bcache() error /dev/vda1: device already registered
[  533.310505] bcache: register_bcache() error /dev/vda1: device already registered
[  533.318959] bcache: register_bcache() error /dev/vda1: device already registered
[  533.374121] bcache: register_bcache() error /dev/vda1: device already registered
[  533.536920] bcache: register_bcache() error /dev/vda1: device already registered
[  533.581468] bcache: register_bcache() error /dev/vda1: device already registered
[  533.589270] bcache: register_bcache() error /dev/vda1: device already registered
[  533.595986] bcache: register_bcache() error /dev/vda1: device already registered
[  533.602638] bcache: register_bcache() error /dev/vda1: device already registered
[  533.651848] bcache: register_bcache() error /dev/vda1: device already registered
[  533.677836] bcache: register_bcache() error /dev/vda1: device already registered
[  533.712074] bcache: register_bcache() error /dev/vda1: device already registered
[  533.717682] bcache: register_bcache() error /dev/vda1: device already registered
[  533.723354] bcache: register_bcache() error /dev/vda1: device already registered
[  533.728951] bcache: register_bcache() error /dev/vda1: device already registered
[  533.777602] bcache: register_bcache() error /dev/vda1: device already registered
[  553.784393] md: md0: resync done.
[  725.983387] INFO: task python3:413 blocked for more than 120 seconds.
[  725.985099]       Tainted: P           O     4.15.0-56-generic #62~lp1796292+1
[  725.986820] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  725.988649] python3         D    0   413    405 0x00000000
[  725.988652] Call Trace:
[  725.988684]  __schedule+0x291/0x8a0
[  725.988687]  schedule+0x2c/0x80
[  725.988710]  bch_bucket_alloc+0x1fa/0x350 [bcache]
[  725.988722]  ? wait_woken+0x80/0x80
[  725.988726]  __bch_bucket_alloc_set+0xfe/0x150 [bcache]
[  725.988729]  bch_bucket_alloc_set+0x4e/0x70 [bcache]
[  725.988734]  __uuid_write+0x59/0x150 [bcache]
[  725.988738]  ? __write_super+0x137/0x170 [bcache]
[  725.988742]  bch_uuid_write+0x16/0x40 [bcache]
[  725.988746]  __cached_dev_store+0x1d8/0x8a0 [bcache]
[  725.988750]  bch_cached_dev_store+0x39/0xc0 [bcache]
[  725.988758]  sysfs_kf_write+0x3c/0x50
[  725.988759]  kernfs_fop_write+0x125/0x1a0
[  725.988765]  __vfs_write+0x1b/0x40
[  725.988766]  vfs_write+0xb1/0x1a0
[  725.988767]  SyS_write+0x5c/0xe0
[  725.988774]  do_syscall_64+0x73/0x130
[  725.988777]  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
[  725.988779] RIP: 0033:0x7fa71a23b154
[  725.988780] RSP: 002b:00007ffec74f2828 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[  725.988783] RAX: ffffffffffffffda RBX: 0000000000000008 RCX: 00007fa71a23b154
[  725.988783] RDX: 0000000000000008 RSI: 0000000002a90030 RDI: 0000000000000003
[  725.988784] RBP: 00007fa71a7366c0 R08: 0000000000000000 R09: 0000000000000000
[  725.988785] R10: 0000000000000100 R11: 0000000000000246 R12: 0000000000000003
[  725.988785] R13: 0000000000000000 R14: 0000000002a90030 R15: 00000000027c4e60