Field styles on Task SLA (task_sla) table have all disappeared/been removed when the instance is upgraded to London release.
Expected behavior as this is an intended change in SLA in London to update to the new Task SLA field styles.
Please see the release notes below in regards to this change in London:
New Task SLA Field Styles
Added field styles to the Task SLA list view, replacing the legacy colored dots with a bar graph which is colored based on the amount of SLA duration that has elapsed. SLAs with 50% or less duration are displayed as green, SLAs between 50-75% SLA duration are displayed as yellow, SLAs with 75-100% duration are displayed as orange, and any SLA marked as breached displays a red bar.