Wet substrate related health problems

What are the potential issues related to the frogs health if the substrate stays wet? My substrates are always wet, I have leaf litter and/or moss on top of most. I was just wondering what I should be looking for. I plan on changing the substrates soon and adding better ventilation, but wanted to be sure/on the look out for any problems caused by them living on wet substrate. Most have been in these terrariums for at least a year. I have one frog that I just noticed is missing toes on one back foot, could be he has always been missing those toes but I can't say for sure; would something like that happen b/c of wet substrate?

Thanks