WiFi dongle not connecting

My WiFi dongle is no longer connecting to the internet - I can't see anything in the GivEnergy app, the web portal or Home Assistant via GivTCP. This is probably related to the fact that I have set up a new WiFi router today, although it did reconnect and worked OK for about 5 hours after I first restarted the router.
I really don't know what to do to fix this and I can't contact by installer because they're no longer in business, so any help would be appreciated.
Thanks

In case it matters, I have an AC3 inverter and 9.5kWh battery.
I have restarted the inverter and have also tried removing and replacing the dongle - this made no difference.
The dongle flashes fast when first connected, then flashes slow and then goes to a constant light, which I thought meant it was connected, but it's still not connected to my WiFi.
I have tried to connect to the dongle's wifi from my phone. It will connect, but the connection drops out after a couple of minutes. I have managed to connect to the dongles configuration page, but the connection isn't good enough to be able to do anything - I'm guessing this means I need a new dongle.
I have checked the house WiFi and there is a strong signal next to the inverter.

I've now got it working. My new router is a TP link mesh system and it seems the dongle won't connect if fast roaming is turned on. I found the answer in this thread
https://community.givenergy.cloud/d/49-mesh-wifi-and-dongle