Regression Resume Lenovo T450

Since some time now CURRENT runs very smoothly on my Lenovo T450 in 
conjunction with drm-stable-kmod installed. WLAN, Suspense&Resume worked 
out of the box (at least ... until now). Due to pkg(8) complaining about 
wrong ABI of packages, I've made an update from r332385 (1200061) to 
r333091 (1200062), and now the T450 does not resume anymore; i have to 
hold the power button for some time to power it down. The 
ZFS-Boot-Environment I've made beforehand updating is still capable of 
resuming.

I tried to find out which commit broke the resume for me by installing 
older kernels, but even installing r332385 kernel (into the actual 
r333091 userland) does not restore its capability to resume.

Any ideas or hints? Which information can i provide to help 
investigating this matter?

-- Manuel