I started my batch of beer on 6-28 fermentation slowed I added dry hops on 7-8 and now it looks like the fermentation has started again what’s going on with it
Most likely CO2 off-gassing due to the dry hop addition.
When should I cold crash it
The common response would be to start crashing when FG is stable over a couple days, not bad advice.
it’s really common for a beer to off-gas when the temp rises.
Warm liquid cannot hold as much dissolved gas as cold liquid can.
I’d leave your batch in for a minimum of 2 weeks, before I’d ever consider racking it, 3 is even better.
Even when the gravity stops falling, the yeast are cleaning up after themselves.
Patience rewards you with fully fermented, clean beers.
As others have said, probably just co2 coming out of solution. That can happen when you dry op and also as you warm the fermentor. Are you watching for bubbles in the air lock? That’s not the best way to check for fermentation activity. Take a few hydrometer readings 2 or three days apart. If there is no change in the FG you are done,