Can't search for users in another forest from any member servers

Question

Hi All

We have forest A that has an outgoing trust with forest B. From the domain controllers - AD users and computers - group - members tab, we can search for users in forest B by changing the location to Forest B. We are prompted for creds for Forest B, once the creds are entered, we can see the users. When we try to add cross forest users to the local administrators group from Computer Management - Local Users and groups -Groups, when we change the location to forest B and search, the search times out. Our networks team have advised that they can't see any traffic being blocked between the member servers and domain controllers and nothing is blocked via the incoming or outgoing NSGs. We have also tried this from a member server in the same vnet and subnet as the DCs and have had the same issue. Any help will be much appreciated.

Forest and Domain Functional level are 2016
DCs and Members servers 2019
outgoing trust to Forest B with Forest wide-authentication

Thanks
Sham