Active Forest Trust Issues - Domain Controller not available.

Hi

I've established a transitive forest trust between Active Directory domains ( lets call them DomainA and DomainB). I'm able to successfully access DomainB objects from member servers and workstations in DomainA (i.e. give DomainB groups file permissions, etc...). However I'm unable to do the opposite in DomainB. For example, if I attempt to give a DomainA group file permissions on a member server in DomainB, I receive the following error:

"The Active Directory Domain Controllers required to find the selected objects in the following domain are not available"

Problem only seems to affect DomainB workstations and member servers. On a domain controller, I'm able to add a DomainA user to a DomainB group.

I've confirmed that DNS resolution is working between the domains, and verified the trust. There is no physical firewall between the DCs, and all windows firewalls have been disabled.

DomainA is running all 2016 DCs, while DomainB is running 2008 R2.

I'm drawing a blank on what's going on.