When making changes to a production survey it is important to make sure the changes are safe to not impact collected data, follow this guide to learn more - https://support.dooblo.net/hc/en-us/articles/208296595-How-To-Make-Safe-Changes-to-a-Production-Survey
Once you have made the changes in the survey the survey version will change. Only once the devices performed sync survey (either if automatic or manual) it will get the latest version and will be able conduct the interviews on the latest version.
Please note that when surveyors will sync the survey, stopped interviews will go to the survey start as possible changes were made to the structure and routing. The answered questions maintain their answers but since the flow/logic needs re-validation the surveyor will need to press the next button several times to get to where the interview was stopped (if the updated logic allows that of course).