Thermal paste conducts heat energy across the microscopic (air gap)surfaces of the processor and the heatsink. It is not water-based and should never dry out (but will eventually) when it does it loses its effectiveness. Don't use cheap paste that dries out relatively quickly.
Does that mean that the problem can be caused by the already dry pasta? a while ago remove the dissipators I cleaned the dry thermal paste they had and then connect the miner after restarting a couple of times started working at its normal power 2000ghs, however, I know that if I restart it is possible to return to the previous state Could it be the thermal paste that is generating this problem? Thanks for your comment!
You always want thermal paste to be still slightly gooey or at least not completely hard and it must also be free of bubbles. A new bead of thermal paste should always be applied after removing a heatsink to safeguard against the inclusion of air bubbles. That's just my two cents on thermal paste and heatsinks I don't know if it will solve your problem.