It started thus:

Jun 18 17:52:45 asus kernel: ata1.00: exception Emask 0x0 SAct 0x2 SErr 0x0 
action 0x6 frozen
Jun 18 17:52:45 asus kernel: ata1.00: failed command: WRITE FPDMA QUEUED
Jun 18 17:52:45 asus kernel: ata1.00: cmd 61/20:08:60:f1:90/00:00:02:00:00/40 
tag 1 ncq dma 16384 out\x0a         res 40/00:01:00:4f:c2/00:00:00:00:00/00 
Emask 0x4 (timeout)
Jun 18 17:52:45 asus kernel: ata1.00: status: { DRDY }
Jun 18 17:52:45 asus kernel: ata1: hard resetting link
Jun 18 17:52:55 asus kernel: ata1: softreset failed (1st FIS failed)
Jun 18 17:52:55 asus kernel: ata1: hard resetting link
Jun 18 17:53:05 asus kernel: ata1: softreset failed (1st FIS failed)
Jun 18 17:53:05 asus kernel: ata1: hard resetting link
Jun 18 17:53:40 asus kernel: ata1: softreset failed (1st FIS failed)
Jun 18 17:53:40 asus kernel: ata1: limiting SATA link speed to 3.0 Gbps
Jun 18 17:53:40 asus kernel: ata1: hard resetting link
Jun 18 17:53:45 asus kernel: ata1: SATA link up 3.0 Gbps (SStatus 123 SControl 
320)
Jun 18 17:53:45 asus kernel: ata1.00: link online but device misclassified
Jun 18 17:53:51 asus kernel: ata1.00: qc timeout (cmd 0xec)
Jun 18 17:53:51 asus kernel: ata1.00: failed to IDENTIFY (I/O error, 
err_mask=0x4)
Jun 18 17:53:51 asus kernel: ata1.00: revalidation failed (errno=-5)
Jun 18 17:53:51 asus kernel: ata1: hard resetting link
Jun 18 17:54:01 asus kernel: ata1: softreset failed (1st FIS failed)
Jun 18 17:54:01 asus kernel: ata1: hard resetting link
Jun 18 17:54:11 asus kernel: ata1: softreset failed (1st FIS failed)
Jun 18 17:54:11 asus kernel: ata1: hard resetting link
Jun 18 17:54:46 asus kernel: ata1: softreset failed (1st FIS failed)
Jun 18 17:54:46 asus kernel: ata1: limiting SATA link speed to 1.5 Gbps
Jun 18 17:54:46 asus kernel: ata1: hard resetting link
Jun 18 17:54:51 asus kernel: ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 
310)
Jun 18 17:54:51 asus kernel: ata1.00: link online but device misclassified
Jun 18 17:55:01 asus kernel: ata1.00: qc timeout (cmd 0xec)
Jun 18 17:55:01 asus kernel: ata1.00: failed to IDENTIFY (I/O error, 
err_mask=0x4)
Jun 18 17:55:01 asus kernel: ata1.00: revalidation failed (errno=-5)
Jun 18 17:55:01 asus kernel: ata1: hard resetting link
Jun 18 17:55:11 asus kernel: ata1: softreset failed (1st FIS failed)
[snip ...] 

Jun 18 17:57:32 asus kernel: ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 
310)
Jun 18 17:57:32 asus kernel: ata1.00: link online but device misclassified
Jun 18 17:57:32 asus kernel: ata1: EH complete
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#15 FAILED Result: 
hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#15 CDB: Write(10) 2a 00 03 
b5 5d 18 00 00 08 00
Jun 18 17:57:32 asus kernel: blk_update_request: I/O error, dev sda, sector 
62217496 op 0x1:(WRITE) flags 0x100000 phys_seg 1 prio class 0
Jun 18 17:57:32 asus kernel: BTRFS error (device sda3): bdev /dev/sda3 errs: 
wr 1, rd 0, flush 0, corrupt 0, gen 0
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#16 FAILED Result: 
hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#16 CDB: Write(10) 2a 00 08 
7b 76 68 00 00 08 00
Jun 18 17:57:32 asus kernel: blk_update_request: I/O error, dev sda, sector 
142308968 op 0x1:(WRITE) flags 0x800 phys_seg 1 prio class 0
Jun 18 17:57:32 asus kernel: BTRFS error (device sda3): bdev /dev/sda3 errs: 
wr 2, rd 0, flush 0, corrupt 0, gen 0
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#24 FAILED Result: 
hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#17 FAILED Result: 
hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#17 CDB: Write(10) 2a 00 02 
90 f1 60 00 00 20 00
Jun 18 17:57:32 asus kernel: blk_update_request: I/O error, dev sda, sector 
43053408 op 0x1:(WRITE) flags 0x1800 phys_seg 4 prio class 0
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#24 CDB: ATA command pass 
through(16) 85 06 20 00 00 00 00 00 00 00 00 00 00 00 e5 00
Jun 18 17:57:32 asus kernel: BTRFS error (device sda3): bdev /dev/sda3 errs: 
wr 3, rd 0, flush 0, corrupt 0, gen 0
Jun 18 17:57:32 asus kernel: BTRFS: error (device sda3) in 
btrfs_commit_transaction:2280: errno=-5 IO failure (Error while writing out 
transaction)
Jun 18 17:57:32 asus kernel: BTRFS info (device sda3): forced readonly
Jun 18 17:57:32 asus kernel: BTRFS warning (device sda3): Skipping commit of 
aborted transaction.
Jun 18 17:57:32 asus kernel: BTRFS: error (device sda3) in 
cleanup_transaction:1832: errno=-5 IO failure
Jun 18 17:57:32 asus kernel: BTRFS info (device sda3): delayed_refs has NO 
entry
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#18 FAILED Result: 
hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#18 CDB: Read(10) 28 00 01 
2b 3b c0 00 00 20 00
Jun 18 17:57:32 asus kernel: blk_update_request: I/O error, dev sda, sector 
19610560 op 0x0:(READ) flags 0x1000 phys_seg 4 prio class 0
Jun 18 17:57:32 asus kernel: BTRFS error (device sda2): bdev /dev/sda2 errs: 
wr 0, rd 1, flush 0, corrupt 0, gen 0
Jun 18 17:57:32 asus kernel: BTRFS info (device sda2): no csum found for inode 
14036317 start 0
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#4 FAILED Result: 
hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK
Jun 18 17:57:32 asus kernel: sd 0:0:0:0: [sda] tag#4 CDB: Read(10) 28 00 01 2b 
3b c0 00 00 20 00
Jun 18 17:57:32 asus kernel: blk_update_request: I/O error, dev sda, sector 
19610560 op 0x0:(READ) flags 0x1000 phys_seg 4 prio class 0
[snip ...]

I shut it down, rebooted with LiveUSB, btrfsck'ed it and ... no errors.  :-/

I fstrim'med it, fsck'ed it once more and ran a smartctl short test.  Still no 
errors.

/dev/sda is an SSD, with /dev/sda2 being mounted as / and /dev/sda3 mounted as 
/home.

I took a fresh back up of /home, just in case, but I don't know what to make 
of the above.  Do you see something familiar in the syslog errors shown above?