There is a set of rectifiers , perhaps selenium type practically appearing like a mechanical assembly. ( few small disks clamped in a bracket and tightened with a screw.and with 3 pins). may be at times two nos of germanium diodes are forming the same. you may replace the with due polarity, by schottkey diodes like 1N5819 or 1N5822.
Once one diode is short, perhaps the meter will read dc in AC range. If the diodes are OK it might read twice its value.
Second possibility, Generally the AC part of the meter will have lower impedance (ohms/volt) compared to DC. perhaps one of the resistors in the series chain has given way and developed high and not full break.
If you have another preferably DMM, you can trace them and locate it.