Is Bonjour working?

I've started using some HomeKit compatible accessories, such as this.

To improve Bluetooth reach I'm also using Eve Extend. All via my Apple TV HD.

Most of the time it all plays nice, but occasionally it will all become unstable and disconnect from the Eve Extend and Apple TV HD. It can then be a struggle reconnecting.

Eve ask if my wifi, which is a BT Whole Home mesh system (which is fast, rock solid and has excellent wifi strength) might be the problem saying:

"the protocol Bonjour, often referred to as mDNS or Multicast... please check with the router manufacturer's support how to make sure it is not blocked at all."

Put simply, the manufacturer (BT) cannot say immediately.

• So... is there a way of testing if aforesaid Bonjour (or mDNS or Multicast) are functioning on my wifi system? (I've seen an Apple Developers' article, but it beyond my limited technical skills!)

• And... if the Eve devices require Bonjour to work, why will they work for a few days, and then not?

Thanks.