I have installed the latest build on two of our company phones. Here my experience:
First Fairphone contained latest fairphone Open OS. Installation all went fine. Problem arised because the phone did not contain a simcard. I set up wifi, but the first time setup allways crashed after the date/time setup and restart itself. I could only get further when inserting a simcard.
Second Fairphone contained normal Fairphone OS, latest build with a quite a few installed apps. I therefore installed Titanium Backup and made a backup of apps and settings on an external sdcard. I installed Lineage and wiped according to description. Start worked, but I could enter the sim pin correctly (T-Mobile Germany). I repeatedly was shown a message, that there was a problem unlocking the phone with the sim. The pin was correct, I tried it a dozen times and did not receive any message that I need to enter a puk. I could also put the sim in a different, also lineage powered non fairphone and there it worked on the first try. I tried it with a vodafone card, which worked perfectly. Retrying the T-Mobile card (which is half a year old and has so far worked without problems in a few different phones). Next problem was that Titanium Backup could not access the simcard (I am sure the sdcard is fine) to reinstall the backuped data and files. Since the T-mobile problem was there to, I reinstalled the backup of Fairphone with Android 6 via backup in TWRP which worked without problems.
Hope this report is of any use. If there are any questions, I will try to answer them. In general: I like it, you have done great work!