The recent backport kernel does *not* have this issue. All is fine with 4.14.0-0.bpo.3-amd64 #1 SMP Debian 4.14.13-1~bpo9+1 (2018-01-14)
This is on a Thinkpad X250 with 00:02.0 VGA compatible controller: Intel Corporation HD Graphics 5500 (rev 09) 4.9.0-4-amd64 and 4.9.0-5-amd64 on the same box do cause screen flickering. Chances are that the issue was introduced by the update to upstream 4.9.46. There are a handful of "drm/i915" changes: https://anonscm.debian.org/git/kernel/linux.git/commit/?h=debian/4.9.65-3%2bdeb9u2&id=17811b5a4b11b32307baca3b88067398a1168cfb "Workaround VLV/CHV DSI scanline counter hardware fail" sounds suspicious, but that's just a guess.
