There can be no good reason for Russian military trucks to be travelling to and from militant-controlled Donbas by dirt roads at night, avoiding official border crossings, unless they have something to hide. It was precisely such behaviour that an OSCE drone recorded late in the evening on 7 August, with the considerable footage showing that the trucks were travelling in both directions.
Source: OSCE catches Russia bringing war to Donbas by night – Human Rights in Ukraine