No mate it's a common occurrence.
In lab conditions both No-Trip and Hi loop test measurements are likely to be similar, certainly within the accuracy of the MFT, but add in the oxidized joints of a typical real world installation and result is likely to be completely different. My money is on the Hi current loop test giving the more accurate result because the higher current is likely to be able to break down the oxide or tarnish film.
The old robin loop tester I have will give you textbook readings when testing an old install! My megger on de-lock is will regularly give readings of 0.8 on a socket where the robin will give you 0.3!
Usually if you push the plug in and out a few times readings improve.
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