Google is going crazy!! My ROAS is down by 50%

I'm pretty new to ads and managing our account which was earlier managed by an agency.

I was able to create a couple of successful (ROAS about ~1.5x) campaigns. They were running well for a couple of months and just a couple of weeks back I increased one of their budget to +20% and for the first day, no impact.

Then my cost per conversion was almost 2x in just 2days.

Not sure why would this happen.

Should I lower down the budget again or just let it be as it is?