Can't always reach HASS from wifi

Hello!

I have a small but annoying issue with HASS. Sometimes (and more often than I would like to) I can’t reach HASS from any wifi device. But at those times I can still reach it from my PC.

My setup is the following:
Router ASUS AC-66U
Raspberry Pi3 + Hassbian + Zwave UZB - connected over wifi, static local ip adress
PC is connected with ethernet cable
Phones are, obviously, connected over wifi - both Android. Galaxy Note 3 with Cyanogen 14.1 and Xiaomi Redmi Pro. And Tablet - surface pro (1). None of them have access to Hassbian - sometimes.

Did anyone else have this issue, is there a way to make it more reliable? Does it matter which wifi I connect with (2.4Ghz or 5Ghz)?

I could not figure out any possible relations between rebooting or something yet. It just becomes “unreachable” for other wifi clients.

Update:
At the same time I can’t reach it’s samba share from PC o.O However it worked before.