Hello,
I have experienced something similar with Aruba and Alcatel Lucent APs. It was actually due to a vendor mismatch on the Operating System
If you can SSH to the Dell APs, run a show version and search for the Operating System manufacturer.
Perform the same operation on the Aruba/HPE AP.
Run some debug commands such as show log debug, show log system, show log kernel and search for vendor mismatch.
If you are actually getting a vendor mismatch, you shouls install the Dell Firmware on the Aruba/HPE APs. That should fix (at least it did in my case)
EDIT: This is meant for IAPs. If you have a controller based network this would probably not apply
HTH