After you synchronise your latest changes, you may find that your browser will often still run an earlier version of your code. This is due to the old code being present in your cache. Try refreshing your experiment start page using Ctrl-F5, Ctrl-Shift-R or equivalent). You may also need to disable the cache via Network conditions in the browser console. When you have developer tools showing you can also press and hold the page refresh icon and select Empty Cache and Hard Reload.
Other alternatives are using an incognito tab or a different browser or device.
Your participants will not normally experience this issue, since they should not have an earlier experiment of your code in their cache, unless they have been helping you pilot your study.