Split sleep

Advice welcome please!

For the past month my 18 month old has started waking for 1-2 hours in the night. He is not upset and does not cry. He is restless and awake. He goes to bed at 7pm and wakes between 6:15-7am. He naps approx 12-1:30. At night he falls asleep independently with his dummy and blanket. When we are out for the day and he naps in the car (unusually only 40m) he will have a more restful night. Could it be too much day sleep causing the split night? Thanks I’m advance for any ideas.