Sudden Drop In ROAS of Shopping Campaign, Help!

I have a Shopping Campaign that has been steadily losing ROAS over the last few weeks. It isn't a huge change. It is down from around 4.58 to 3.42 (WoW) in the last 3 weeks. Although I'm trying to figure out why, I saw a very sudden drop this last weekend.

ROAS was 4 on Friday and then suddenly dropped to 2.42 on Saturday to 2.23 on Monday. This sudden drop has scared me.

When I studied the data at a product level I can see that one product suddenly dropped to 2.51 on Monday from 4+ the other days. This same product is the biggest drop even when we see the week on week trend that I mentioned earlier. Now this is our best seller and is basically carrying this multi million dollar brand. So naturally a big part of the budget goes to this product. So how do I manage this situation. I cannot pause it as it actually isn't bad, itt has a good ROAS but it is falling and that's affecting the whole account.

What can I do? It is a TROAS campaign so I cannot even control this product at a bid level. So im unsure how to improve the performance of this campaign.