My sister runs a bagel place in Denver and she had the exact opposite happen, her Mondays got crushed for like two months and then just went back to normal out of nowhere. Turns out some big office nearby had a Monday remote thing and then changed it. So it might not stick, hard to say. If it has been three weeks that is a real pattern though, three weeks is not a fluke. I would maybe bring in one extra person for a few Tuesdays and see, worse case you are out a little cash, best case you stop drowning. Saturdays dipping is the part that would bug me more, that used to be the money day for everyone.