WAX610 firmware update über ios browser

I am operating four WAX610 for more than one year. three of them were bought in 2023 and the last one this year. netgear insight app indicates that the last WAX610 device (insight's one-year support still applies) has the latest firmware version 10.8.6.3. The other devices (which are no longer insight supported) have an older firmware version. direct connection to the devices via browser has worked in the past in order to update the devices manually. but not anymore and I don‘t know why. connection via browser works fine. When I try to update the formware, I get the message “last firmware version” even though Insight says “new firmware version available” under each of the three „older“ device. how can I update the fw? I tried it with the latest iOS version and safari browser but I don‘t think that this is the problem. is a firmware update no longer possible without an insight subscription? that would be extremely unfair.