The inverters only work on the 2.4GHz wifi network, not 5GHz and with some networks it tries to prioritise pushing devices to connect to the 5GHz which the inverter can’t do so it fails to connect. The fix to this is to turn the 5GHz network off, let the inverter connect, and then you can turn the 5GHz back on.
But this is usually just an ‘initial connect’ problem, sounds like you’re getting more general connection issues.
It sounds like signal strength. You can login to the inverter’s wifi (details in the wifi dongle setup guide on the knowledgebase) and do a scan for networks to see what signal strength it is receiving. Turning off the 5GHz might improve things but more likely you’re going to need to put a wifi router or booster nearer the inverter.
TP link do some good wifi repeaters. I used to use a power over ethernet repeater which worked OK but about once every couple of months it would just loose connection. In the end I bought a Mercusys Mesh network (cheaper version of Deco) and its been very solid and stable throughout the house and garden. Price of them on Amazon varies a lot though.