Monthly 2-hour MOTN wake ups

My 14 month old is generally a good sleeper, but once or twice a month will wake up scream-crying and won't go back to sleep for 2+ hours. I usually give him Motrin after 20 minutes of crying because I assume it's teething-related but he'll still cry for at least another hour. Doesn't seem like night terrors (and I think he's too young) and it isn't happening at the right frequency to be a sleep regression. I already reached out to our ped and she said teething is her best guess as well. What else could be causing this? Has anyone else's kid done this?