I have encountered this problem twice, once in a Beogram 1800 and once in a Beogram RX-2.
When the PLAY button is engaged on the front of the machine it acts like the CUE button has been engaged. Tonearm moves to the edge of the album, the platter spins appropriately but the arm stays up. When CUE is engaged, the arm drops and it plays the album.
If PLAY is engaged and then disengaged 1 or 2 times consecutively it will start appropriately. That is; platter starts, arm moves to the beginning of the album and lowers.
Where do I start? From my review of the schematics, this doesn’t seem like a likely fault. Much less experience it in 2 separate machines.