In short, it’s the nature of Republic’s service. Republic numbers are indeed Voice over Internet Protocol (VoIP). Republic’s use of VoIP is part of the nature of its’ blended WiFi/cell service.
Some service providers object to VoIP numbers because according to the FCC, they are landlines (wireline is the more correct industry term) and these providers believe VoIP numbers are incapable of receiving text messages. There is nothing Republic can do to change this regulatory classification. As you know, your Republic number is fully capable of receiving both calls and text messages.
Other service providers believe VoIP numbers are a security risk. They are wrong about this, however, Republic cannot control the policy decisions of others.
You might consider asking the service providers in question about whitelisting (making an exception for) your Republic number. Some will do so, others will not.
With that said, I’ve moved your post into an already existing discussion on the topic.