There are free wifi analyzers for all phones and laptops. Use it to make sure your mesh channel is strong AND not congested with neighboring signals.
Also, if you notice this starts after some time using, try a fan on the devices. Sometimes the issue is overheating. It sucks but all these devices are built rather cheaply and high power, high speeds + encryption all create heat and if the device isn't ventilated or have appropriate heat sinks they can still overheat. Things have gotten a little better but I had so many brands do this in the early days of Wifi that I always consider this a possibility.