Midsummer and some EXT4 failures on SSD on my Dell. I just swapped my Samsung 850 PRO to older Intel 530 SSD due latest TRIM related issues when this happened. (EDIT: check link, how promptly Samsung reacted to this SSD related post of Algolia!).
Under pretty heavy development load with virtual machines, I run upgrade to system and after reboot I couldn't connect to Wifi. I thought that there is an issue with signal (like some times before) - but this was not the case. Whole wifi interface was gone. It turned out that system was unable to load firmware to wifi card and it failed due this.
Couple of reboots later, system came up with read only file system and I saw the reason. EXT4 errors on my Intel SSD, reason unknown.
Update: Ended up changing SSD to rotating HD, before checking reasons for this behaviour. I also dis-enabled /etc/cron.weekly trimming from couple of SSD equipped Toughbooks, just to be safe side, if it's about TRIM failures on SSD's.