A filesystem is mounted read only usually by system when it's detected to be 'dirty' ...it needs check and fix errors. The issue may be 'soft' and you can fix it with appropriate fsck or 'hard' that the underlying disk/flash is corrupted.
In your case I'd try serial console and log the entire boot and see where an error jumps out.
I'm my time with ER-X I've experienced one unit that had defective FLASH and the simplest and cheapest solution was to throw it to trash and buy new one.
EDIT: Sorry, I've now realized that you've attached dmesg output. ...not sure why the system switched to r/o and what the errors mean.
UBIFS error (pid 2094): read_znode: bad key order (keys 2 and 3) UBIFS error (pid 2094): read_znode: bad indexing node at LEB 93:3272, error 6 magic 0x6101831 crc 0x4aaf0ee8 node_type 9 (indexing node) group_type 0 (no node group) sqnum 751546 len 188 child_cnt 8 level 0 Branches: 0: LEB 1261:100496 len 4144 key (10530, data, 23) 1: LEB 1261:106496 len 4144 key (10530, data, 24) 2: LEB 1261:110640 len 4144 key (10530, data, 25) 3: LEB 1261:114784 len 4144 key (10530, inode) 4: LEB 1261:118928 len 4144 key (10530, data, 27) 5: LEB 1237:0 len 4144 key (10530, data, 28) 6: LEB 1237:4144 len 4144 key (10530, data, 29)UBIFS warning (pid 2094): ubifs_ro_mode: switched to read-only mode, error -22