I ask because depending on the setting to perform after the CRED is submitted, different things happen.
I suspected it's "keep displaying this form"
This sometimes causes issues, because the Form is actually still displaying but might be hidden in a Modal or whatsoever. In some cases, mainly when the Modal or PopUp Codes (HTML / JS) are not correct, this can push follow up HTML down or up.
I have had this issues in past.
I solved by removing my code and ensuring a clean Modal or PopUp, and often, it's better to redirect to some page or post, in case you can afford this on your project.
You must also observe, keep displaying the Form usually keeps the Form URL Slug in your Browser bar.
This is not always desired.
Nonetheless, it should be possible to achieve your goal in a satisfying way.
Please let me know it the Theme is the problem here.
I suggest a local copy of your site where you inca play with other themes and setups
You will quickly find out where the problem is.
If this repeats with other themes and no other plugins but CRED/Toolset, please inform me.
I will then probably need to request Access, and see this live on a debuggable Website.
For this I will enable Private reply, in case after all needed and suggested tests, the issue persist.
Please acknowledge that I can not debug a Custom Theme or issues surgeon from other Plugins, therefore I would need a access to a clean basic and minimal site, where the problem is reproduced.
Thank you