Anchor and Tag restarting

I am having some problems when testing the DW1000. I have 1 anchor and 1 tag and there seems to be packet loss between the two during the Two way ranging. It is working fine for some time and then suddently on decawave no longer receives information for the other. Is there maybe a minimum delay that I should have between transmissions?

Those 2 x DW1000 are they on an EVB1000, DMW1000, DWM1001-dev or your own design?
And how are they powered? If by battery, maybe the battery is nearly empty.