Thank you for writing in, please do a testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it's fixed, you'll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time. And please clear your caching plugins before you deactivate it.
Also navigate to Settings > Permalinks and save it without changes.
If nothing works, please provide us login credentials in a secure note as your site is in under construction so we can take a closer look.