joint ESA claim

I have a client who is in receipt of Employment and Support Allowance he is the lead claimant, 6 months ago his partner had to go into hospital she stayed here for 6 months, cl made ESA aware of this change at the time.
His partner has now moved back in to the house.
I have tried to explore if any changes have been made to the ESA award since his partner was in hospital, the client is unsure.

Would his partner moving back in trigger a migration to Universal Credit or would ESA just update the circumstances and the award for the client.

Any advice would be great
Thanks

ESA couple claimants can have temporary separation of up to 52 weeks and remain entitled so there shouldn’t have been any change to amount paid, nor does partner coming home again mean there is any need to move to UC.