Why is part of my home electric going out?
With both 240 and 120v devices having a problem I would first call the power company and report the problem to them. 
Usually they will preform a service safety inspection for free (they don’t want a fire in their gear).
Then I would check the type of panel there 2 brands known to have these problems the first is federal pacific (FPE) the stablock model of breaker is known to fail (to the point I will only remove them). The other is zinsco , I haven’t seen the extent of problem on these but others have reported.

If neither of these brands one thing I will do is turn all the small breakers off, then cycle the main breaker on and off 10-20 times. This cycling the main breaker can clean carbon off the hammers in the breakers and reseat them For a temporary fix.

If you feel comfortable remove the dead face or front cover from the panel and look at the main feeds looking for overheating damage (I would expect your electrician at least did this).

Providing us with a photo of the panel and model number we may come up with additional possibilities if the utility comes up with nothing, but most of these failures I have seen have been on the utility side other than a few main breaker problems or rule of 6 “main” for the lower section.