Possible workaround, reported this to Rockstar:
*** rant ***
And tried to post on Reddit but it won't let me because karma is too low, aka "no noobs allowed!", and messaging it to the mods just got me muted for 3 days, lol, pointless as I couldn't post anyway, feels very elitist and unwelcoming, no more Reddit for me.
*** end rant**
After doing "A quiet time" and "who is not without sin" right after, I no longer have access to my weapons other than the revolver I'm carrying. I died once during the first mission and went straight to the second after that, so not sure where I lost the weapons. I did notice reloading any save, even from before either mission, did not help.
Also I noticed that it was simply the L/R 2 buttons not working, as the revolver slot said 2/3. None of the slots on the 1st and 2nd page allowed me to use L/R 2.
I got it to work again by bringing up the weapon wheel, going to the 3rd page (horse), there on my outfit slot I could use L/R 2, after that on any page and my weapons were selectable again.