I seem to have just experienced this exact symptom on my RB2011UAS-RM.
Prior to this I was noticing that the LCD screen was not responding to swipes and this morning I noticed 100% CPU Usage. My next thought was to perform a reboot (via winbox) and now I am stuck in a boot loop. I get up to the stage where the screen shows boxed for Interface, Stats, Stat Slideshow, etc. and then after a few seconds it reboots. Oh and I am experiencing the gigabit ports not negotiating a giagbit link with a gigabit switch too.
My RB2011UAS-RM is (was) running RouterOS v6.4 and has been operational for just over a week. My configuration should not have been at all stressful for this router.
The cure apparently is to use Netinstall to recover the router, but if I have to do this every week (even ONCE is bad enough)... it will be going back!
This is my own personal router for home, so it's not a mission critical device. I work in an industry where failure of equipment can cost a LOT of money so I am used to things being perfect. My old Cyberguard/Snapgear router has been in service for over a decade.
I thought after my very positive experiences over the years with an RB750, RB951 and a pair of RIC/522 5.8GHz outdoor routers that the RB2011UAS-RM would also be good... so far this seems NOT to be the case.