Last night several of the lights and outlets went dark in the house. Then
it mysteriously came back by itself for a few hours, and now these circuits
went out again. All fuses tested ok (unless there is a failed circuit
breaker somewhere). One of the dead circuits is an outlet that is right
below the main panel (so it's not a fuse or breaker in a remote subpanel).
Looking into this further, I tested the voltages going into a subpanel that
is right next to the main panel.

The difference between the two hot phases going into this subpanel show
110v. Between one of the hot phases and neutral it is 120v. Between the
other hot phase and neutral it is only 12v!

Last year the electric company came out to fix a broken neutral wire on the
telephone pole, and this reminds me of the floating neutral problem I had
back then, causing mysterious problems with some of the circuits. Because
there is a major difference between the different phases and the neutral, I
wonder if I should call out the electric company again, maybe their original
repair failed?

Or could this be due to a wiring problem inside the house that I should
check first? Or perhaps a failed circuit breaker in this subpanel?