There is an extremely rare bug in the virtual classroom caused by image gradients, you'll notice the classroom responding extremely slowly or potentially booting you. This has happened in 0.000001% of sessions, but if it happens to you it is due to the following:
All slides are automatically converted to PDF when uploaded. This ensures a high-quality display of all content (as evidenced by the ability to zoom into the slide without loss of quality on fonts and drawings). However, if your slide has a large background image that has a very smooth transition, such as this one, it might cause problems when displayed in the client.
If you are using such as smooth gradient, test it first. To test, upload your slides to a practice session and try advancing through them. If the client becomes very slow, or unresponsive, on a particular slide, then edit the slide deck to take it out, or take a screenshot of the offending slide and replace the slide deck with the screenshot. Save the presentation and try uploading again for a test. Advance through all the slides and confirm there are no other pages that cause delays (if there are, replace them as well).
The web conferencing platform already has checks for such slides, but it if you are using a slide deck that has smooth gradients, it's good to test ahead of time to make sure.