Puppy who is not at all crate trained is suddenly going into crate?

My seven month old neutered puppy was not crate trained. We tried to the first few weeks when he was 8 weeks old but he ”won” and we gave up. He would occasionally go into his crate when we were training him – totally voluntary and the only time he cried in it was at night. He liked taking naps in it but nights were miserable.

We ended up keeping the crate out in our living room and in the last few days he’s been going in it and taking 2-3 minute rests and then coming back out. He is otherwise totally normal and happy. My partner is worried he’s sick or there is something wrong with him.

Any insights is appreciated!