Shaking, glitching app; custom designed in conflict with template

I built this app for my company using Anvil. We wanted to have our own design that is aligned with company’s design element, therefore, I added a lot of our own css code. This has caused our app to experience unwanted glitching and shaking movements on certain page, as you can see in the gif in the link.

This is the clone of our app: Anvil | Login

Since it contained a lot of internal information, I had to disable most functions and make it a proxy app. The behavior you see in the gif may not be experienced by all users; on my browser, I had issues at the DASHBOARD page. Allow me to write a short walkthrough if you want to explore the pages here:

Dashboard page

  • On the first dropdown, choose the 2nd option
  • After the 2nd dropdown appear, choose the 2nd option
  • Press "Toon Dashboard

Analyse page

  • Click on the orange button on the left
  • On the first dropdown, choose the 2nd option
  • Click Ga verder
  • A new page will appear, called Woningtypes
  • On the 1st dropdown, choose the 2nd option
  • 2nd dropdown, 2nd option
  • Fill in Nieuw scannaam anything
  • Click Ga verder
  • A new page appears
  • First (only) dropdown, choose 2nd option

I hope that problems can be noticed without having to walk through this. This issue is really unfortunate because it makes the app looks really weird and using it unpleasant. Please let me know if you have any questions, and I appreciate any help possible!