2 volume groups and no Xraid

I can't attached the log, but here is a copy/paste of it.

Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
md126 : active raid6 sda3[11] sdf3[6] sde3[7] sdd3[8] sdc3[9] sdb3[10]
15608675328 blocks super 1.2 level 6, 64k chunk, algorithm 2 [6/6] [UUUUUU]

md127 : active raid6 sdb4[0] sde4[3] sdd4[2] sdc4[1]
15623471360 blocks super 1.2 level 6, 64k chunk, algorithm 2 [4/4] [UUUU]

md1 : active raid10 sdb2[0] sda2[5] sdf2[4] sde2[3] sdd2[2] sdc2[1]
1569792 blocks super 1.2 512K chunks 2 near-copies [6/6] [UUUUUU]

md0 : active raid1 sdf1[6] sda1[10] sdb1[9] sdc1[8] sdd1[7] sde1[5]
4190208 blocks super 1.2 [6/6] [UUUUUU]

unused devices: <none>
/dev/md/0:
Version : 1.2
Creation Time : Fri Jun 15 09:34:07 2018
Raid Level : raid1
Array Size : 4190208 (4.00 GiB 4.29 GB)
Used Dev Size : 4190208 (4.00 GiB 4.29 GB)
Raid Devices : 6
Total Devices : 6
Persistence : Superblock is persistent

Update Time : Fri Jan 7 06:47:54 2022
State : clean
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0

Name : 2fe67fe8:0 (local to host 2fe67fe8)
UUID : f5237630:c64bb4be:4fed641f:b3365079
Events : 1057

Number Major Minor RaidDevice State
6 8 81 0 active sync /dev/sdf1
5 8 65 1 active sync /dev/sde1
7 8 49 2 active sync /dev/sdd1
8 8 33 3 active sync /dev/sdc1
9 8 17 4 active sync /dev/sdb1
10 8 1 5 active sync /dev/sda1
/dev/md/1:
Version : 1.2
Creation Time : Wed Jan 5 13:22:16 2022
Raid Level : raid10
Array Size : 1569792 (1533.00 MiB 1607.47 MB)
Used Dev Size : 523264 (511.00 MiB 535.82 MB)
Raid Devices : 6
Total Devices : 6
Persistence : Superblock is persistent

Update Time : Wed Jan 5 23:51:58 2022
State : clean
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0

Layout : near=2
Chunk Size : 512K

Name : 2fe67fe8:1 (local to host 2fe67fe8)
UUID : 6243d5a4:9492aa54:4687fe9f:751334fc
Events : 19

Number Major Minor RaidDevice State
0 8 18 0 active sync set-A /dev/sdb2
1 8 34 1 active sync set-B /dev/sdc2
2 8 50 2 active sync set-A /dev/sdd2
3 8 66 3 active sync set-B /dev/sde2
4 8 82 4 active sync set-A /dev/sdf2
5 8 2 5 active sync set-B /dev/sda2
/dev/md/Data-0:
Version : 1.2
Creation Time : Fri Jun 15 09:46:36 2018
Raid Level : raid6
Array Size : 15608675328 (14885.59 GiB 15983.28 GB)
Used Dev Size : 3902168832 (3721.40 GiB 3995.82 GB)
Raid Devices : 6
Total Devices : 6
Persistence : Superblock is persistent

Update Time : Fri Jan 7 06:48:35 2022
State : clean
Active Devices : 6
Working Devices : 6
Failed Devices : 0
Spare Devices : 0

Layout : left-symmetric
Chunk Size : 64K

Name : 2fe67fe8:Data-0 (local to host 2fe67fe8)
UUID : 84dfd3a6:cd9b72d9:45a515b8:1310b289
Events : 44955

Number Major Minor RaidDevice State
11 8 3 0 active sync /dev/sda3
10 8 19 1 active sync /dev/sdb3
9 8 35 2 active sync /dev/sdc3
8 8 51 3 active sync /dev/sdd3
7 8 67 4 active sync /dev/sde3
6 8 83 5 active sync /dev/sdf3
/dev/md/Data-1:
Version : 1.2
Creation Time : Fri Jan 22 09:02:00 2021
Raid Level : raid6
Array Size : 15623471360 (14899.70 GiB 15998.43 GB)
Used Dev Size : 7811735680 (7449.85 GiB 7999.22 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent

Update Time : Fri Jan 7 06:48:35 2022
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0

Layout : left-symmetric
Chunk Size : 64K

Name : 2fe67fe8:Data-1 (local to host 2fe67fe8)
UUID : deb6a4dd:c5b46702:1226c73e:928b7ffb
Events : 441

Number Major Minor RaidDevice State
0 8 20 0 active sync /dev/sdb4
1 8 36 1 active sync /dev/sdc4
2 8 52 2 active sync /dev/sdd4
3 8 68 3 active sync /dev/sde4

Multiple RAID groups are how the NAS takes care of drives of different sizes.  You definately don't want to be removing any (which you'd find very hard to do, anyway), as they both contain your data.

Did you turn off XRAID in an attempt to manually expand the volume?  If so, you've run into an unfortunate (and, I believe, unnecessary, perhaps even a bug) restriction about going back to XRAID.  Even though your volume was created by XRAID, the NAS just doesn't bother to see if it still meets XRAID criteria and a switch back is possible (or, perhaps, incorrectly determines it doesn't meet the criteria).  It didn't always do that, but I don't know when it was introduced.  But now that you're in FlexRAID mode, you're doing an expansion (incremental drive size increase) FlexRAID doesn't support.  There is an SSH command that will likely do it, but let's see that mdstat.log first to be sure.