This would only happen if you have a huge number of forms(history versions) and your farm is so slow.
Do the following troubleshooting steps:
- Try to clear your browser cache, hard clearing and check.
- Try restarting your farm.
- Check it out another site where there is a few number of forms or a new site “this would be even better”, to make sure this is not something related to the solution itself.
- Open in Chrome, hit F5 and check for any errors in the console tab.
- trim of the history version so it does not get too large:-
Open the SPARK Forms Builder hidden templates list:https://youdomain/site/subsite/lists/sparksettings
click on list settings, versioning settings and check the “Keep the following number of versions” option and set the max number of versions you want to have like this: