AC intermittently doesn't cool
I would suggest listening to your unit when it is running , not just the fan but the compressor also. Possibly make a recording  I am talking about the outside unit.
When the unit is not cooling try listening and recording again,
The problem could be as easy to fix as an intermittent contactor (a contactor is a high power relay that turns on the compressor) some units have different relays for the fan and compressor so listening is important, the compressor not humming away may indicate it is “sticky” or possibly the starting cap is getting close to failure.
A cap going bad normally causes dimmed lights and hard starting it’s hard to explain the sound but it can take 10-15 seconds when normally it is up to speed in 3-5 seconds.  When the start capacitor fails it may blow the fuse or circuit breaker. Or it may over heat the motor and the mother’s internal thermal overload turns it off until it cools.
If I was called for a intermittent cooling issue I usually check the cap they are a cheap fix and look at the contactor and see if it has been throwing excessive arcs.
Other things like bad valves in the compressor can be the problem but if your technician put a gauge set on it that would be obvious.
One of the last things of the top of my head would be the thermal expansion valve on the evaporator (inside coils) these can stick closed and prevent refrigerant from flowing so the outside unit starts pumps up to shutdown pressure then waits for a cycle restart timer 3-7 minutes on most systems.
Edit:
You might ask your tech if he measured the cap or inspected the contactor. (Both are in the outside unit).
At this time your ears are thallus you’re best troubleshooting tool.
Intermittent problems are hard to find because everything is running when we get there.