Can't connect to certain PC's through Wifi

I am a member of a local makerspace. We use beaglebone to run our Lasersaur laser cutter. That being said, we have had a couple years of issues with various connections that doesn’t make any sense. For example, sometimes when a new person comes in and logs on to our network, the lasersaur page will not load, and pinging the IP says it cannot reach host. That being said at the exact same time I can get it to pull up on another PC without a problem. Then it will sometimes not connect to the PC is was working with… This doesn’t make any sense to me, because no one changed anything and it was working before… What gives!?