I think there may be a bigger issue in thurgadin / icewell going on (perhaps other zones), last night I re-checked Lorekeeper Gundlt and his responses were all working (Krystorf was still not responding to 'writ' line of text however). I checked my log from when I made this post and Lorekeper Gundlt was definitely not responding (was not sneaking or invis).
Odd that it is now working, and coupled with Telin receiving a Councilor Amberfeld response when I was not and the Loremaster Sarl anomaly described
here leads me to think there is some kind of scripting bug / memory problems with the NPCs.
I think there was a quake recently, so perhaps that reset Lorekeeper Gundlt and others and got their responses working?