I’ve never used TWRP to update my FP or whatsoever with it, so I can not answer to your question.
I’ve always only used fastboot and/or the update app.
Well, the link below explains that, I was on 17.04.3 (published during few minutes by mistake last week) and I’ve updated to 17.04.8, the update was a bit more complicated that before, but when everything is clear (and thanks again to @retsifp) , it’s easy and my FP2 works perfectly with Android 6.0 FP 17.04.8.
I’ve done all the updates from day one (February 2016), never lost any data, and always rooted my phone each and every time.