i915kms broken at some commit between r296485 and r297692?

I'm running FreeBSD 11.0-CURRENT r292595 on ThinkPad T430 (i7-3520M,
Intel video 4000). Today I tried to update to a fresher version.
Something has been broken somewhere between r296485 and r297692, 
I suspect namely i915kms - it won't boot: at the boot screen I see that
all modules are loaded, then after "Booting..." message at the bottom
screen turns black in 1-2 seconds of booting process, it seems to be the
point when it regularly switches to native resolution.

Can somebody shed light on it? What can I check to get more info on
this?

Regularly I update to the revisions used to build snapshots at: 

ftp://ftp.freebsd.org/pub/FreeBSD/snapshots/ISO-IMAGES/11.0/

assuming that those revisions have less issues. So tried a few, including
the head. None worked for me after a certain revision (from the range I
mentioned above).

Thanks for advices!

Sergey