I needed to re-add one of my Tradfri switches: TRÅDFRI Kabelloser Dimmer, weiß - IKEA Deutschland
I don´t use the switch within the Phoscon App, but use inputs for HomeAssistant. Means there are no groups to activate lights within the webapp.
Since I have added the switch again and push the button once, all lights switch on, but just virtual and not the bulbs itselfs.
You will be able to identify the Group number in Home Assistance, which might have changed if you re-included it.
You might also consider making a dedicated group in PWA and use that for control from HA instead as that will work even if the remote runs out of battery.