This is a known issue on SketchUp for web. Numerous threads exist already which you can find easily. The team is working on a fix so be patient.
Thank you.
My work around is to make my dimensions and/or labels into a group. When they are blocked out, I select the group, right click, cut the group with the scissors icon, and then paste in place. The dimensions then reappear. You do not edit or update if it’s a scene. Just leave it alone once they reappear. It happens on all my scenes. You can check some out in the screenshots - Models by Royce.