10.0.21 is no longer a supported version of Skuid, I definitely recommend upgrading at least to 11.2.30 in sandbox and seeing if this has any affect. I know specifically of one major issue addressed between 10.0.21 and 11.2.30 which affected performance in Lightning:
Performance degradation for Skuid pages in Lightning
In Salesforce’s Winter ’20 update, some of the Lightning Locker overrides of the document API had an unexpected effect on jQuery.
jQuery’s selector engine mistakenly flagged some APIs as not supported in the browser. This, combined with other recently discovered performance issues in Lightning Locker, caused significant delays when using jQuery selectors in custom code and in certain key areas of Skuid’s action framework when running in Lightning Locker.
We have patched our version of jQuery to be more compatible with Lightning and Salesforce’s Winter ’20 changes.
Best practices for upgrading
Best practices for upgrading can be found in Upgrading Skuid on Salesforce. As a reminder, Salesforce does NOT allow reverting back to prior versions of managed packages. Skuid always recommends installing new versions in a non-business critical sandbox environment to test all mission critical functionality before installing into a production environment. We also recommend that you update out of date themes after you upgrade. Please let us know if you continue to encounter any problems with this issue after upgrading.