Each IP checker uses a different IP database while checking your IP. That's why you may get different results on different websites. Unfortunately, many of these databases provide inaccurate information about IPs. Some of these IP checkers offer IP blacklist checks. For instance, you can easily find your own IP address on a blacklist. Besides that, blacklists retrieve information from various IP databases which may lead to a misconception about a particular proxy provider.
The only way to find out how often a blacklist is updated is to contact the publisher directly. We assure you that even if you find an IP address on a blacklist, it will not affect your performance in any way.
SOAX uses the MaxMind IP database, which is why we suggest referring to our own checker in order to identify IP addresses.