HP Switch not connecting back after losing connectivity to a Meraki Switch via a 4 port LAG

Quick overview:

Core switch is a Meraki L3 Switch that connects all Access Points, Servers, and internet Routing. There is a four interface LACP going to the HP Switch, which is where all desktops and phones connect to.

When the Meraki Switch reboots for Firmware Updates, the HP Switch will not renegotiate the LAG back to the core Meraki without being rebooted.

Any idea why this would be the case?