Just in case it hasn't been mentioned here, there appears to be and issue with LACP bonds created via NetworkManager where the LAG won't get established after reboot. I spent too much time troubleshooting this on my Fedora 35 Server and my new Mikrotik CSS326, convinced the switch was the problem.
Apparently, the issue affects several Linux distributions that use NetworkManager. This Github issue explains the problem and workaround:
https://github.com/systemd/systemd/issues/15208
Basically, you can create the file
/etc/systemd/network/98-bond-mac.link
with the following content to allow the LACP bond to be established after a reboot:
[Match]
Type=bond
[Link]
MACAddressPolicy=none
Or simply remove NetworkManager and create/ manage interfaces manually, which has been reported to also fix the problem.
I opted to create the 98-bond-mac.link file.