pfSense

Test case:

1x Netgate SG-2440 (pfSense 2.2.6)
1x Cisco SG-30028 managed L2 switch
2x Client laptops, plugged into the switch

On each client laptop, a ping to their respective gateway (the pfSense node, both client nodes are on different VLANS. Each VLAN is configured on LAGG0) keeps running for the duration of the test case.

Configuration:
pfSense:
- igb1+igb2+igb3 in 1 LAGG named 'LAGG0'
- LAGG configured in LACP mode

Cisco switch:
- GE22+GE23+GE24 in 1 LAGG named 'LAG0'
- LAGG configured in LACP mode

Reproduction steps (see attached screenshots for visual confirmation):
- Login to pfSense web interface
- Click on 'interfaces'
- Click on LAGG
- Edit an active LAGG configuration
- Remove or add a parent interface from or to the LAGG
-- In my scenario, I removed igb3 from the LAGG0 configuration
- Click on save

Result - after clicking on save:
- The running pings from the client laptops to their gateways (the pfSense node) stop immedeately
- pfSense seems to not be participating anymore in any of the VLANs configured on the LAGG
- the LAGG seems to have stopped functioning alltogether

Steps to fix it:
- Restart the pfSense node