Since it sometimes "works for one hour", that suggests you have the right adapter.
I've read that newer versions of macOS are picky about transmission errors – as in, they don't want to see any, and will cut resolution or cut the signal if they detect errors. Maybe the "hydra" cable on your Thunderbolt Display is a bit flaky – not enough to keep it from working (after a fashion) with the old Mac, but enough to make the new Mac want to cut the signal.
You could try getting a Thunderbolt 1/2 cable (Mini DisplayPort connectors, but higher-quality cable) and running it from the TB2 side of the Apple TB3-to-2 adapter to the TB daisy-chaining port on the Thunderbolt Display. Maybe bypassing the "hydra" cable (and leaving it unused) would be a workaround for the problem.