11 month old wide awake for 2 hours in the middle of the night

Split nights at this age are almost always a total-sleep issue, she's getting enough sleep across 24 hours so her body just decides 1-3am is awake time. The fix is usually cutting day sleep or pushing bedtime later. 2.5 hrs of naps + early bedtime might be a touch too much now.

We had this exactly at 11 months. Trimmed daytime nap by 30 min and pushed bedtime from 7 to 7:30, and the night wakings disappeared in about 4 days. She just didn't have enough sleep pressure to make it through the night with that much day sleep.

Keep it boring during the awake window, no playing, no picking up, dim and dull, so she doesn't learn that 1am is fun social time. We made the mistake of engaging at first and it reinforced it. Treat it like night even though she's happy.

Also worth checking she's not approaching the 2-to-1 nap transition, around 11-14 months some babies need less day sleep and the split night is the first sign. Capping that second nap helped us bridge toward one nap.

Update from when we were in this: it was 100% too much day sleep for our girl. Capped naps at 2 hours total and shifted bedtime 30 min later. The 2am party phase was gone within a week. Try the schedule tweak before anything else, it's the usual culprit.