Root file system mounted as read-only

Recently, on of our Ubuntu 18.04.1 LTS servers went into RO mode. I have searched all over and tried various things to no avail, therefore I am turning here for help.

I copied a folder (size +/ 24 MB) on a server running Ubuntu 18.04.1 LTS using: cp -r /opt/3.5.0 /opt/4.0.0. Right after, the system went in read-only mode.

It is an mSata SSD. The disk has 16GB out of 29GB available, so a full disk should not be the cause.

The syslog:

Mar  3 10:08:11   kernel: [6633028.028328] sd 1:0:0:0: [sda] tag#21 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_TIMEOUT
Mar  3 10:08:11   kernel: [6633028.028337] sd 1:0:0:0: [sda] tag#21 CDB: Write(10) 2a 00 02 d8 13 a0 00 00 b0 00
Mar  3 10:08:11   kernel: [6633028.028341] print_req_error: I/O error, dev sda, sector 47715232
Mar  3 10:08:11   kernel: [6633028.028371] sd 1:0:0:0: [sda] tag#17 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_TIMEOUT
Mar  3 10:08:11   kernel: [6633028.028377] sd 1:0:0:0: [sda] tag#17 CDB: Write(10) 2a 00 02 d8 0e 60 00 05 40 00
Mar  3 10:08:11   kernel: [6633028.028381] print_req_error: I/O error, dev sda, sector 47713888
Mar  3 10:08:11   kernel: [6633028.028393] EXT4-fs warning (device sda2): ext4_end_bio:323: I/O error 10 writing to inode 1442150 (offset 0 size 778240 starting block 5964426)
Mar  3 10:08:11   kernel: [6633028.028399] Buffer I/O error on device sda2, logical block 5832908
Mar  3 10:08:11   kernel: [6633028.028408] Buffer I/O error on device sda2, logical block 5832909
Mar  3 10:08:11   kernel: [6633028.028414] Buffer I/O error on device sda2, logical block 5832910
Mar  3 10:08:11   kernel: [6633028.028420] Buffer I/O error on device sda2, logical block 5832911
Mar  3 10:08:11   kernel: [6633028.028426] Buffer I/O error on device sda2, logical block 5832912
Mar  3 10:08:11   kernel: [6633028.028432] Buffer I/O error on device sda2, logical block 5832913
Mar  3 10:08:11   kernel: [6633028.028438] Buffer I/O error on device sda2, logical block 5832914
Mar  3 10:08:11   kernel: [6633028.028444] Buffer I/O error on device sda2, logical block 5832915
Mar  3 10:08:11   kernel: [6633028.028449] Buffer I/O error on device sda2, logical block 5832916
Mar  3 10:08:11   kernel: [6633028.028455] Buffer I/O error on device sda2, logical block 5832917
Mar  3 10:08:11   kernel: [6633028.028666] sd 1:0:0:0: [sda] tag#16 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_TIMEOUT
Mar  3 10:08:11   kernel: [6633028.028672] sd 1:0:0:0: [sda] tag#16 CDB: Write(10) 2a 00 02 d5 62 c0 00 02 b0 00
Mar  3 10:08:11   kernel: [6633028.028675] print_req_error: I/O error, dev sda, sector 47538880
Mar  3 10:08:11   kernel: [6633028.028684] EXT4-fs warning (device sda2): ext4_end_bio:323: I/O error 10 writing to inode 1442161 (offset 0 size 180224 starting block 5942404)
Mar  3 10:08:11   kernel: [6633028.028738] EXT4-fs warning (device sda2): ext4_end_bio:323: I/O error 10 writing to inode 1442165 (offset 0 size 172032 starting block 5942446)
Mar  3 10:08:11   kernel: [6633028.028802] sd 1:0:0:0: [sda] tag#7 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_TIMEOUT
Mar  3 10:08:11   kernel: [6633028.028808] sd 1:0:0:0: [sda] tag#7 CDB: Write(10) 2a 00 02 d5 5d e8 00 04 d8 00

This continues for another second and then no more logs are written.

Whenever I try to do anything on the system (for example tab-completion) I get an error regarding r/o, for example: cannot create temp file for here-document read-only file system.

I have rebooted the system in recovery mode, and ran fsck. Right away I see an error message. When looking at the status of systemd-remount-fs.service I see:

systemd-remount-fs[1343]: mount: /: mount point not mounted or bad option
systemd-remount-fs[1343]: /bin/mount for / exited with exit status 32

I have also tried using sudo mount -o remount,rw /dev/sda2 / but with the same error message as a result.

My etc/fstab file:

UUID=xxx    /           ext4    defaults 0 0
UUID=xxx    /boot/efi   vfat    defaults 0 0
/swap.img   none        swap    sw       0 0    

From various answers online I understand I should set the fsck order, but as the system is in RO I am not able to update the file.

When I run mount -l I see (amongst other things, but I don't think it is all relevant): /dev/sda2 on / type ext 4 (ro, relatime, data=ordered)

Not sure if it is relevant, but while in recovery mode I go to system-summary I see under LVM state:

Physical Volumes: not ok (BAD)
Volume groups: ok (good)

So there are a few questions I have. Apologies if I am asking anything obvious, I am quite new to all of this.

1. First of all, do you have any further advice on which steps to take to get out of RO mode?
2. Is this more likely a software or a hardware issue?
3. As we have more systems with the same setup, I would like to understand why my copy action could have triggered the system going to RO. I have done this before on other systems without any problems. The folder contained a .Net application that was running at the moment of copying, could this be the cause?

Thanks for your help!