Tree-checker Issue / Corrupt FS after upgrade ?

[<benjamin.haendel@gmx.net>]

Hi,

i have been running my little Storage (32TB) on a Ubuntu 18.04 LTS Machine
with btrfs-progs 4.17. I then did my monthly upgrade (apt dist-upgrade) and
after a reboot my Partition could not mount with the error message: 
"root@Userv:/home/benjamin# mount -r ro btrfs /dev/mapper/Crypto
/media/Storage
mount: bad usage"

I then proceeded to run a btrfs check which gave thousands of errors and
then also a super-recover:
root@Userv:/home/benjamin# btrfs rescue super-recover -v /dev/mapper/Crypto
All Devices:
Device: id = 1, name = /dev/mapper/Crypto

Before Recovering:
[All good supers]:
device name = /dev/mapper/Crypto
superblock bytenr = 65536

device name = /dev/mapper/Crypto
superblock bytenr = 67108864

device name = /dev/mapper/Crypto
superblock bytenr = 274877906944

[All bad supers]:

All supers are valid, no need to recover

I now checked my dmesg log:
[45907.451840] BTRFS critical (device dm-0): corrupt leaf:
block=22751711027200 slot=1 extent bytenr=6754755866624 len=4096 invalid
generation, have 22795412619264 expect (0, 207589]
[45907.451848] BTRFS error (device dm-0): block=22751711027200 read time
tree block corruption detected
[45907.451892] BTRFS error (device dm-0): failed to read block groups: -5
[45907.510712] BTRFS error (device dm-0): open_ctree failed

Google inquiries to this topic led me to this link:
https://btrfs.wiki.kernel.org/index.php/Tree-checker
It tells me to mail here first so thats what i am doing. I kind of suspect
since everything worked perfect (Memtest also no errors) before the update,
it has to do something with that update. I am wondering if it would help if
i deleted my OS Disk and reinstalled an older Version of Ubuntu, like
16.04.6 LTS ?

Since then i upgraded to 20.04 LTS with BTRFS-PROGS 5.7 as a lot of forum
entries said it would be wise to use the newer versions as older were buggy.
That brought no help as well.

Since i am no Linux/Unix Expert i thought it might be better to ask now
first as advised in the link above before proceeding with any other plans.

I find it hard to believe that all data is gone, i feel its buggy behavior
as the partition and everything is still there:
root@Userv:/home/benjamin# btrfs fi show
Label: 'Storage'  uuid: 46c7d04a-d6ac-45be-94cc-724919faca2b
Total devices 1 FS bytes used 28.23TiB
devid    1 size 29.10TiB used 29.04TiB path /dev/mapper/Crypto

Best Regards,
Benjamin Händel