Migration to UC from IR ESA

hello!, I received my letter to migrate from esa to UC which I completed on 26th March 2025. I was last paid on the 22nd on March before I migrated and then I was paid the full amount again on 5th April 2025 (I am due to be paid on a Monday every two weeks but it always hits my bank on the Saturday before) I have just now (wed 9th April) received a payment of £18.38… and a bit confused. Is this the 2 week run on payment? As it’s a very small amount? I understand I was paid on the 5th April but I thought that it is paid in arrears so that payment would cover the 2 weeks prior before I migrated. Any help is much appreciated