My site is deployed within China and when users log in within China, it is very slow, taking about 15 seconds, but outside of China there is no problem.
I tried a fresh install of WHMCS 8.2.1 but still have the same problem, and since I can rule out the module aspect (since no modules are installed after a fresh install of WHMCS), I tested WHMCS 7 at the same time and it works fine without any problems!
I don't know which services it networks with during the login process?
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