Lights intermittently flicker in whole house.

Our lights intermittently flicker in whole house and have been doing so for about 3 weeks. Since it is intermittent, it took us a while to figure out what was going on and that it was not related to any appliance or the furnace. Week 2 we called the utility company and after 2 calls they came out an inspected the outside lines. Of course they sent the guy out in the evening. Anyway, he noted the neutral was secure at the line into the meter box and he said he tightened the connections at the pole. He said to check with the neighbors to see if they have the same problem. Checked with the neighbor who shares the same drop from the transformer and they do not have any flickering. During week 3 (today) had an electrician come out to look at our boxes and the meter box. He came out around noon on a bright day. He tightened a somewhat loose neutral and the main panel and then tightened another item in a sub panel. He also made sure that all other connections were secure. He also checked to see that the connections in the meter box were secure. None of the panels nor the meter box exhibited any signs of corrosion or arcing. I was present when he was doing the work. When dusk hit, I noticed that the lights across all circuits continue to intermittently flicker. The flickering pattern seems to be random in timing and length. One point of reference. The sub-panel controls all of the lights in the house across multiple circuits. The main panel came to play when a previous home owner in the 80s had an attached garage added, which was between the pole and the prior main panel (now the sub panel).

Looking for any advice on the next course of action to take.

Flicker Shine unsteadily; vary rapidly in brightness: "the interior lights flickered and came on".

What I would call flicker someone else might dimming or brightening.

There are many reasons why lights will flicker, inductive loads coming on line, loose connections in the hot conductor, loose connections in the neutral conductor ect.

When it is due to loose connections in the neutral some of the lights will dim while others will brighten.

Had a 2nd electrician came out today. He tested the voltage and noted it was pretty even coming in. He torqued down the lugs in the meter box. Inspected both the main and sub panel. On the main panel, the main breaker would not shut off (hoped the 1st electrician would have checked that). They are ordering a new main breaker and will install it when it comes in. The box was installed in the 80s and is a 200 amp cutler hammer panel. Should the main breaker be hard to find? Hopefully when the new main breaker is installed it will take care of the problem.