[Moto X4 ROMs, Kernels, Recoveries, & Other Develop] EntropyZer0:
Phone and SMS not working

I have never had any problems with Lineage in the past, so I'm not sure about the bug reporting/ support process here. I think this is the right place to post, but if not, please direct me to where that would be ;)

(I will also post a bug report on GitLab once I'm done here, but this seems more active so I'll start here.)

I have just flashed the most recent nightly on my Moto X4 (XT1900-07) and after fiddling with a few GCam versions to get the wide-angle-lens working (Arnova's Advanced 1.4 is working for me, in case anyone searches this thread for those keywords), I thought that everything was working. What I forgot was that this is a phone:

Neither telephony nor messaging work, mobile data however does.

Telephony:

Calling out results in the regular phone conversation screen opening, but then there isn't even the regular dialling sound, much less any actual connection.

Messaging:

The integrated messaging app doesn't seem to even have a way to initiate new messages; When I click the little "+" in the corner to start a new conversation, I can chose the recipient(s), but then there is no button to confirm those and start composing an actual message. Trying to start a different SMS app (I tried Next SMS (the successor to Handcent) and, technically, Super Backup as it restores old messages by setting itself as the default SMS app) immediately crashes said app.

Neither incoming calls nor messages arrive at the phone.

What I tried so far (to no avail):

Deleting Cache/ saved data for the messaging app (and for Next SMS too, just for good measure).

Checking APN settings: They were already correct. (Had to check by hand; config message by the provider obviously didn't go through.)

Choosing a different Preferred network type: The default is "Global", but no combination of GSM, WCDMA and/ or LTE (I am in Germany on the O2 network) changes anything: Mobile data works, phone and SMS do not.

The SIM status looks alright to me (Connected, In Service, voice and data have either LTE or whatever type I restricted them to in above step), with the exception of the field "Phone number on SIM", which is "Unknown". Although I am not sure whether that ever displayed anything different.

Booting into safe mode.

Scouring the internet for people with similar problems - didn't lead to any useful hits beyond what I tried already :-/

(I noticed the advice "settings>network & internet>mobile network>advanced and uncheck the default 'enhanced 4G LTE Mode'" in several posts; however, this option does not exist for me. (Not as in greyed-out but as in no-such-item))

Any help would be greatly appreciated :)

Edit: I probably should specify: This is lineage-16.0-20190415-nightly-payton and I have never had 15(.1) on this phone, so I cannot comment on whether it worked with that or not. Probably will try it later today though.

Edit2: After trying both lineage-15.1-20190224-nightly-payton-signed.zip and lineage-16.0-20190410-nightly-payton-signed.zip I can confirm that the messaging problem is specific to 16.0-20190415, as it works fine in both. The other issue seems to be broader though - I cannot make or receive calls on either of those versions.