The problem is that the function that should return the network hashrate for one of the three mining algos, calculates the average hashrate using the nChainWork "Total amount of work (expected number of hashes) in the chain up to and including this block" which includes the work of all three algos and if I see correctly even also PoS work.

This is also the reason why all the returned network hashrates for the three different algos are always almost the same even though their difficulties vary a lot.