As of this writing, applying a background color using a gradient through conditional formatting of a numeric (DECIMAL or INTEGER) column in a Table visual causes the table to render with the message:
The data type of a field used in this visual has changed too much for QuickSight to automatically update your analysis. You can adjust field data types by editing or replacing the current dataset.
This is a new issue that has appeared in recent days and is affecting a QuickSight dashboard that was published months ago and used heavily just last month.
As a workaround, I've removed conditional formatting from all columns in the table, and the table is now successfully rendering.
Here is an example using a subset of the data in a new analysis:
And here is the same table once a gradient is applied to one of the columns. The issue appears regardless of the column type chosen.
After finding the QuickSight-specific community, I've cross-posted this issue to https://community.amazonquicksight.com/t/background-gradient-for-numeric-column-breaks-table-visual/8890.
This issue appears to be resolved now.