Hello @HUMPHREY Adam (1IT/CLD) ,
There should be no impact if the configuration is correct & accepted by all the backend pools. What I mean here is all the 20 sites should be able to accept the same healthprobe settings such as protocol, path etc. If they require different protocols & paths, then it could cause an issue.
Also, any updates to backend pools are seamless and will cause zero downtime (if the new configuration is correct).
Please refer : https://learn.microsoft.com/en-us/azure/frontdoor/front-door-faq#how-long-does-it-take-to-deploy-an-azure-front-door-does-my-front-door-still-work-when-being-updated
Kindly let us know if the above helps or you need further assistance on this issue.
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