That's odd – I wouldn't expect WhatsApp to use the phone number for any internal routing-related decisions (or as anything other than an account identifier in general). If it's a routing issue, that could explain the problems being localized, but I wouldn't expect the actual account phone number to have any bearing on it.
I've had no issues using it all day across several countries for both calls and texts.
I've had no issues using it all day across several countries for both calls and texts.