Much of the below is from an e-mail sent by UBNT. Always test your updates in a controlled environment. The problem is crashes and hwnat offloading.
We received a lot of crash reports of ER-X, ER-X-SFP and EP-R6 with latest firmware v2.0.1 when hwnat offloading is enabled.
Discussion can found on community forum here -> https://community.ubnt.com/t5/EdgeRouter/EdgeMAX-EdgeRouter-software-version-v2-0-1-has-been-released/td-p/2730981
We removed v2.0.1 for ER-X, ER-X-SFP and EP-R6 from http://download.ubnt.com portal, now latest stable version for those models is v1.10.9 We removed v2.0.1 for ER-X, ER-X-SFP and EP-R6 from UNMS portal and new instances of UNMS will not be able to download this firmware anymore. However this firmware will still be available in local UNMS cache if it was updated before April 10th, 2019
Suggestions for ER-X, ER-X-SFP and EP-R6 users:
If you don’t use hwnat offloading and don’t experience random reboots then you safe to keep using v2.0.1 firmware If you use hwnat offloading then you are adviced to roll back to previous stable version v1.10.9 firmware If router has been bricked after random reboot and factory reset does not help then you have following options: If router is still on warranty then you can RMA bricked router here -> https://rma.ui.com/ Or if router is out of warranty then you can try restoring v1.10.9 firmware via console as described here -> https://help.ubnt.com/hc/en-us/articles/360018189493-EdgeRouter-Manual-TFTP-Recovery (You can find console instructions here)