Hmm a couple of thoughts here:
Pausing campaigns for a while often means the algorithm has to go through its learning phase again, so a dip in performance is normal when you restart. But for performance to tank completely sounds like something else is going on.
You've tested a lot on the ad side, so I'd stop looking there for a bit and look at your funnel instead. Check your metrics to see where people are dropping off.
Getting clicks but very few landing page views? Maybe the site is slow or something is broken.
Lots of product page views but no adds to cart? It's probably an issue with your product page. Check the pricing, product photos, or the description. You mentioned 'changes in the business'—did your pricing go up? This is often the main culprit.
Loads of adds to cart but no one buys? Something is putting them off at checkout. Unexpected shipping costs? Not enough trust signals? I remember one ecommerce client we worked with, a subscription box company, achieved a 1000% return on ad spend on Meta Ads, but their success was massively dependent on a smooth, trustworthy checkout process.
The "changes in the business" bit is the biggest clue here. I would seriously review every single thing that's different now compared to two months ago when it was working well. It's probably not the ads.
Hope that helps!
