Why those my app or doesn't acknowledge my new personel best on of my last ride?

Can you share the activity?

Do you have a previous record for that record? I've experienced that sometimes if no record has been set it will not set the record. The solution is to set the record manually from an activity in Garmin Connect Web. After that new records will be set.

I already have one then made a second one that was register then a 3 third and this one doesn't register 

How do you know it was a personal best?

Set it manually.

Well when you know your average speed on a 40 k is 24.3 and this one is 25.1 and the time is mear 2 min shorter im pretty sure it is!!