So if you can connect with a device, then the wifi is working, if the wifi was not working you would not be able to connect with any device at all.
So its a device issue rather than a wifi issue.
Some devices can be a bit erratic and inconsistent when it comes to connecting to wifi, printers are known for this, and in fact my printer often needs to be reset, eg: switched off, wait 30 seconds, then switch back on again, before it connects.
So maybe try switching the devices that are not connecting, off, then on again.
I've also had phones in the past that seem to "forget" the wifi connection, even though its still there, and by deleting the wifi connection,(on the device) then setting it up again, sorts it out for a while....
Could also be a wifi coverage issue I suppose, eg: if the devices are in different parts of a building, and some parts get better wifi coverage than others, so maybe try moving things around, can also consider moving the wifi bridge, router, etc to a more central location or get one of the many wifi boosting devices?