big spaces and decreasing font size

At our association website, we use WordPress with the divi builder. Since a few months, it makes big spaces and decreases the font size. If we edit a page, and we hover with the mouse over a box we want to edit, it jumps from small to large, which makes editing difficult since you never know where the text would end up and how big the font would actually be. The new posts we created since then managed with the problems as good as possible, but all the old ones are also affected by the current problem, so the posts look totally shattered.

I have discord, skype and zoom, so I can share my screen. I need a mentor to help me fix the problem and maybe would love to give me advice from time to time. The website is called selbstliebeverein.de.