Rightly proper to look into this anomaly before it becomes
serious. If nothing else, fixing a problem before it happens
can only be a good thing. Using that extension cord and meter
does do one thing important. For example, proving all
interrupted devices were on one phase, then empowers a utility
crew to repeatedly check only one spot until they find
something. If ailed devices are on both phases, then the
utility crew is encouraged to on a neutral wire problem - a
failure that may eventually get destructive if not found.

IOW by obtaining that one little additional fact, then a
utility crew has better reason to play more aggressively
(concentrate their attention) only on those live wires that
can explain your 'unique' symptoms.

In specs for computers (for example), a 100% loaded computer
must keep working when power is lost for 16 msec. All will
typically keep working even longer. If voltage drops so low
that incandescent lumens are less than 40%, then a computer
must still work just fine. These are characteristics defined
by specs for computers. Other devices such as digital clocks
may not be so resilient. I said seconds. Not full seconds.
Milliseconds. Every device will keep working a fixed period
after power is completely lost. Some just work longer.
Computers tend to be some of the more resilient to dropouts.
Some clocks tend to withstand dropouts longer. Some clocks
may have a battery or internal capacitor so that short
interruptions don't bother them.

But again, determine if all 'interrupted' appliances are
only on one phase or both. A utility crew would be more
likely to aggressively shake the suspect live wire rather than
uselessly checking all. That information also tends to make
them more believe you do have an intermittent problem.

Choreboy wrote:
Here are facts. An interruption too brief to see even at night will
knock out my phone clock, microwave clock, and computer. The problem at
my neighbors' was conspicuous in daylight as the lights went on and off
for several seconds. My house was fine. I'd say the problem did not
affect the transformer output terminals.

Here's another fact. The reason my neighbor checked the bedrooms was
that in her experience, any time she had to reset the stuff on one side
she would also have to reset the bedroom clocks. She was amazed to find
them working.