Intermittent connections like this, that work sometimes and don't other times, are usually related to loose wires. Plugging or unplugging something in the outlet wiggles it enough that the wires connect or disconnect.
This is something that you SHOULD fix -- loose wires tend to heat up, and could possibly start a fire in the wall.
Luckily, it's usually something you can fix yourself. Basically, turn the power off, check the outlet to be sure it's really off, then unscrew the outlet and pull it out from the wall, and check all the wires to be sure they are solid.
For wires connected to side screw terminals, check that the wire is looped around the screw securely and that the screw is tight.
If you find any 'backstab' connections, where the wire is plugged directly into a little hole in the back of the outlet, remove them and convert them into connections on the screw terminals. (They were used for a while, but it's been found that over time they tend to come loose. So most electricians don't use them anymore.)
Sometimes there are short wires from the outlet, connecting to other wires in wire nuts inside the box. For those, you need to check both the outlet connections, and then the connection in the wire nuts, too. Take the wire nut off, make sure the wires are twisted together tightly, and put the wire nut back on securely.
You will probably find an obviously loose connection -- a wire might even come off entirely when you pull the outlet off. But don't stop after fixing that -- continue to check the rest of the outlets where you've had a problem. If one connection came loose, the others are just as old and might also be loose. Check 'em all while you;re there with your tools.
But you might get all through this and not find any obviously loose wires. But put everything back in the boxes, turn the power back on, and test it. I've sometimes found that it now works reliably -- I managed to fix it, just by tightening everything up, without noticing a real loose wire.