Why am I experiencing currency conversion issues in my online store?

Hello,

My store often shows incorrect prices, mostly being -%20 until you get to check-out. Sometimes it’s a lot worse.

i have 3 Markets set up (UK, USA, International).

i also have ‘Enable Custom Theme Currency Converter Enabled’ (this is the only cause i’ve noticed because when i disable it, then the store prices become correct for me… but im worried it will be incorrect for others outside of UK)

Please help. (pictures to demonstrate)