Rate limiting DNS requests form a single IP?

Dose NextDNS rate limit or slow down request form a singles IP if it breaks a certain threshold? We are a K-12 Education account with 6000 students. We have13 sites each with 1 Gig fiber terminating at a 10 Gig connection at our county office of education.  Each site has a unique single IP linked  to NextDNS and making  all DNS requests for the site. When under normal load certain web sites (politico  avery bestbuy trigger the issue repeatedly) will resolve at the web at the address bar but content will not load for 3 to 20 seconds. This only happens mid day when we are under normal load and If we change our DNS to alternate like Google or Quad 9 or test after school is out the problem goes away. In our NextNDS logs there is no blocks shown and we have even tried removing all NextDNS flitting and security options incase something was getting hung up. We have tried a Debian server with the CLI and a windows but both with the same result. Any help would be greatly appreciated we love the platform.