Hi eberrick,
Firstly the following article gives a checklist of process to remember when replacing a stack unit and it does depend on whether the unit being replaced was master unit or not but may help you check for issues that were overlooked.
https://gtacknowledge.extremenetworks.com/articles/Q_A/How-do-I-replace-a-faulty-unit-or-management-...
was the replacement unit identical to the old one ? If not you may need to address the config mismatch using :
https://gtacknowledge.extremenetworks.com/articles/Solution/Securestack-Config-Mismatch-When-Replaci...
From "show switch" i would check that the Management status is Mgmt for the replaced unit and the others are stack member , preconfig model id matches the Plugged in Model id , switch status is ok for all and code versions all match.
Also check "show switch stack-ports" to make sure there are no errors on the stacking ports.
Check "show switch status" to make sure the status is FULL and the admin state ENABLE.
If this all looks ok and stack integrity looks fine then i would check manually that the config actually on there is the same as the old one. Maybe there is something missing.
Assuming your uplinks are a lag i would check the lag status and stp status for issues.
If you have further issues it may be worth opening a case with us.
Hope this helps
Glyn