Guild Wars 2

I’m getting drastically different results when retrieving the gem exchange at different times (using the same sample query of 4000 gems).

For the URL https://api.guildwars2.com/v2/commerce/exchange/gems?quantity=4000
I got

{"coins_per_gem":2203,"quantity":8815104}

Then some minutes later I redownloaded the JSON and got

{"coins_per_gem":2201,"quantity":220180}

and finally again

{"coins_per_gem":2172,"quantity":869157}

—

As for the coin endpoint
https://api.guildwars2.com/v2/commerce/exchange/coins?quantity=1000000 (100g) gives

{"coins_per_gem":3236,"quantity":618}

while the in game exchange shows that 100g gives you 458 gems instead of 618 like in the JSON