Doesn't sound to me like it is anything to do with having dropped the nap if it was 2/3/4 months ago.
It is likely developmental. Very many people here notice sleep disturbance close to the birthday and half birthday and this happens for years. At this age your LO might be fearing the dark, you could try a little night light. He might be having a little separation anxiety (which you are responding to which will comfort him, see if you can add some power to his lovey if he has one by adding special mummy/daddy hugs and kisses to it to power it up for over night use). He may be having a language leap.
All you can really do is continue as you with the reassuring, verbal if it works, go in for a quick hug if needed etc, until this passes. It will pass.
If he is tired from the NWs you could give an opportunity for one nap, maybe he will nod off in the car or stroller for a few mins or invite him for a one-off nap, if he says yes then he needs it (I would just do one as you have clearly worked out his routine needs already but this sleep disturbance is similar to handling illness, people whether young or old can need a bit extra sleep through a tricky time and may sleep in the day if very tired). If nap is a total no-go then you could do a one off EBT at say 5.30pm.
It is not essential to offer a nap or EBT because really if he is tired he can sleep longer in the morning but if you feel OT is building then you might want to try.
hope this helps