What mistakes or bloopers have you noticed in the show?

The same woman walking her dog in the same outfit outside the perimeter, likely just a repeated establishing shot but I see her

Boom mics in the earlier seasons. You can see a mic in Matt’s pocket when he’s at Paul’s house and finds his wife dead.

I think in Season 1 Jane said she was an only child.  Few episodes later Syd shows up. 

In season 2 when Amanda cuts her vacation to Hawaii short to return to work, her hair is different in different scenes the same day. Bangs when she’s in her office, and no bangs with center part when she’s not in her office.

One that comes to mind is in the later seasons, Megan's hair is straight when she's at Peter & Michael's office, then she goes to the hospital & all of a sudden her hair is wavy & very big.

I recall an editing mistake in Season 4, Ep 22 “Run Billy Run.” After Billy sleeps with a competitor in order to find out their pitch for the same airline campaign, Amanda takes a call at work in front of everyone to see if they got the account or not. The way the shots were edited together makes Amanda’s celebratory reaction seem premature. Other than that I can think of seeing microphones a few times like others already said.

Casting Coop.

there’s a scene where you can see the mike overhead. I can’t remember who it’s with

I’ve been watching season 5 again and remember another blooper at Jane’s Boutique. One of the outfits merchandised for sale at the shop is a memorable outfit Sydney wore herself in another episode so most likely the wardrobe department just used costumes for the clothing in the store 🤭 Or I guess it still could be explained at least that maybe Jane designed that outfit for Sydney and is now just selling the same look 💁‍♂️