I never get SMS text spam on my phone. Installed Lineage OS on a Samsung Galaxy S4 mini phone. I installed TWRP and LOS both from official website (not various links on google or XDA). Installed F-droid (with privilege extention).
I only had a handful of apps installed: Fennec F-Driod, Firefox Focus, Stocks Widget, Net Guard, net Monitor, BlueBourne Scanner, Termux, SnoopSnitch and Yalp,
Phone was running without a SIM for about a week. All was OK until I inserted a SIM. Moment I insterted the SIM a got spam from a load.
Note I have used the same apps (except for Fennec) on another phone without a single spam SMS!
So is the nightly infected with malware or spyware?
Beware of post hoc, ergo hoc : it's not because you started getting spammed after installing LineageOS (+ apps) that it DID cause the spam.
Since LineageOS (any many if not all the apps you cite) is open-course, it's highly doubtful that it's infected (that's the point of open source software !). Also, have you asked on the LineageOS community channels (Reddit, IRC, of XDA forum) if anyone has the same symptoms ?
I've set up a Galaxy S4 Mini with pretty much the same apps as you, and did not get such a spam.
My take is that for some reason, your phone number got leaked to a spammer during the time of your LineageOS transition. I think the cause lies elsewhere.