That counter was designed to be powered from a radio's internal 9-Volt regulator. Packaging it in a plastic box invites folks to power it from 13.8 Volts or more. This overheats and degrades the 5-Volt regulator. That chip drops about 4 Volts when built into the radio. The drop will be twice that if it's powered from 13.8, and this doubles the heat load on the regulator chip.
Don't know which of several production versions is in your counter, but popping the cover and reading the output of the 5-Volt regulator when it does this could reveal the cause if it's dropping or showing quirky noise when probed with a 'scope.
A meter alone won't tell you if funny noise pulses are coming out of the regulator chip.
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