Quick question as a long term roadie who has just got back into MTB.
Brand new freshly waxed chain in the Yorkshire mud. Just under a 2 hour ride, dry but everything covered in mud so cleaned whole bike with water and a bike spray and wiped chain dry.
Reckon it’ll be ok or need a re wax?
I’d rewax or at least do a drip on wax after a mud ride
The Dylan Johnson YouTube video that @blind76 is referring to actually touched on this. Josh was presenting his finding that you cannot rely on how a chain feels or sounds.
Context: He was pointing this out with regard to how a chain might sound or feel quieter, immediatly after applying a oil lubricant. It just creates a grinding slurry.
Mud = reset contamination for smooth running in future. You may at this point realise why lots of us have at least three chains per bike!
Do you change chain after every muddy ride then? I’ve two MTB chains at the moment 
Pretty much, it’s a judgement call and if it’s not too bad I might drip wax on top, but for the work vs reward it’s always better to swap/rewax the chain.
Do people take any precautions to protect the wax when washing their bikes?
Generally if my bike is dirty enough that it needs to be hosed down, it’s likely dirty enough that I should re-wax the chain. The exception to this might be if it was just a pretty dusty gravel ride but not major mud/dirt. In this instance, I might lightly hose the bike down and just make an effort not to get the chain wet. I’m not worries about a little mist over over spray, but I would avoid like a hard spray directly at the chain.
If the chain does get wet, be it on a ride or washing, it’s important to wipe it dry afterwards to prevent any flash rust, even if you plan on re-waxing before your next ride. I bought some of the Silca gear wipes and have been pleased with their intended usage on the bike/chain post rides.
I use a waxed chain on my gravel bike but I am also unashamedly a fair weather, good condition rider so pretty much the worst is washing the dust off with a hose then regular soapy water clean and re-dip every 300km or so.