There is visual evidence someone removed the knock-outs exposing the hot side of the main breaker and then filling the lugs with a substance that looks like oakum. Didn’t touch as not knowing if it could conduct current. This area would be live until the meter was pulled. At least the last one like this had duct tape over the knock-outs for Pete’s sake.
My guess is that it’s duct seal. Looks like it covering the breaker lugs that should have been behind the KO’s on the cover.
I wrote it up as a safety issue to be repaired by Sparky