For some public API endpoints there is a few-seconds cache based on transients. For example, if you check json-api.php you will see that some responses are cached for the amount of seconds specified by the wallets_exchange_memoize_seconds option.
When there is no object cache installed, WordPress falls back to storing the transients on the options table. If there is an object cache installed the transients are stored on that. This is not the first time I see someone with an object cache experience problems with transients not expiring. After a quick search on the web it seems this is caused by misconfiguration of the object cache, although I’m not sure.
To check, can you clear your W3 Total Cache, or memcached, or whatever it is you’re using? Does this refresh the output of the APIs?
You should also be aware that DB rows of transients do not necessarily get deleted just because they are expired. WordPress does some garbage collection but it is not perfect, so third-party solutions exist to clear expired transients from the DB to save space. In any case, the WordPress transients API should not return expired transients even if they exist on the DB, assuming this is where they are stored on your system.
I can always add a switch to disable cache, but we should at least have some idea of what is going on here. The question is why your transients are not expiring. For example, the transient that stores output of the get_market_summaries call is wallets_exchange_summaries and by default should be cached for 5 seconds.
Please do let me know if you find anything about this.
kind regards