This is "you getting discouraged" after the first try
I get it, repairs are frustrating, meeting repairpeople is a disruption to your day, claims are intimidating; they're designed to be, to deter frivolous claims. But you have to do them.
It is the nature of intermittent problems that iteration is required to fix them. Because the problem is intermediate, there is no way to do an immediate test: the first attempted repair must be "given a trial" for several times as long as it typically takes to fail.
The most efficient way to handle this is for the electrician to leave, for you to observe, and then, for you to report.
This is when emotions take over. The customer is annoyed that it wasn't fixed the first time, as if my 2nd paragraph did not apply to them. Declares the last repair person incompetent. Never wants to see them again. Is fed up and frustrated with the process. Etc. etc. blah blah. Direct result: the "report" part never happens, and the iteration is interrupted.
You are here.
So branch it anyway you want: a) ignore it, b) bring the free home warranty person back in (believe me, they hate go-backs too), c) hire your own person at your own expense to start the iteration all over again, or d) do it yourself and start your own iteration.
The risk with "taking it on yourself" is after the first iteration fails, you are now obliged to fire yourself, leave yourself a scathing Yelp review, and never allow yourself back in the house again :)
Most likely this thing is...
Builders love to work FAST. If you've done any skilling up in the electrical department, you know that there are 2 (well, 3) ways to attach a wire to a receptacle:
- wrap a J-hook around a side screw and tighten all to spec
- jab a straight wire in a hole and done
- use $3 devices instead of 50 cent devices, place wire(s) in the 2 holes under a screw, and tighten the screw.
One guess which one builders use. This "backstab" method is notorious for causing exactly this sort of problem - and it's usually an expensive, tedious bug hunt. This is why most of us kill backstab connections on sight and convert them into one of the other two.
The worst of it is, backstabs are un-inspectable. You can't check screw torques or see signs of arcing. For this reason, I like to wrest the wire out of the backstab, pulling firmly while twisting maybe 90 degrees, so I can inspect the wire for any pitting from arcing. Also it preserves wire length, which is precious.
Backstabs do have one virtue: they are hard for the worker to screw up. Screw connections, on the other hand, are very vulnerable to being mis-torqued - usually under-torqued. They set up booths at electrician trade shows, and invited electricians to torque screws to spec (without a torque screwdriver). They also tested electrician's companions (wives, office assistants etc.) Both were awful, but both were equally awful, in same proportion of under/good/over torqued. NEC was revised to require torque screwdrivers.
Gold standard advice: you probably have at least a 50% chance of solving this simply by converting all your connections on receptacles and switches from backstab to one of the other types of connection. However, I must recommend a torque screwdriver, because it would defeat the purpose to add as many bad screw connections as you remove bad backstabs!
It's also possible for "wire nut" connections to be screwed up, but the "wire 5 houses a week" type Romex-spider electricians usually get those right. Just give them a pull test: hold the nut and firmly tug each wire. That all but assures a good connection. If there's tape holding the nut together, that's a crutch for someone who couldn't pass a pull test.
Lastly it's worth checking the breaker connection and the neutral wire connection inside the service panel. That last one blind-sides even the experienced experts (who have already checked everything else).