Copied my website to make updates with all in one wp migration - something does not work

For larger update, I made a subdomain and copied my website to there with All-in-one WP Migration extended.
I made a new validation for this site .
All is there, but on the front end the side doesnot show. When I want to open a page with PRO, it shows a strange page that tells met to login again (session expired) - but that brings me into a kind of loop.

I have the idea this is a small thing, but could you please help me with this - what is incorrect in this site? Thanks. I will send you the inlog also.

Ahh, I think I already know why. The WP version is too low… perhaps. I will upgrade it to 5.4.
If I have any troubles … I will come back to you.

Hello @lvandeemter

Thanks for writing to us, please feel free to write to us if you have any concern.

Have a great day!

Thanks, it was the WP version indeed. It works great now. Thanks

Hi @lvandeemter,

Glad that we are able to help you.