DOM API Changes May Require UI Test Updates
Why: We’re calling out the fragility of these tests due to changes as Lightning Experience continues to evolve with modern web standards. We understand the value that you gain from automated UI testing and the maintenance burden these changes put on you. Salesforce has never guaranteed backward-compatible HTML, CSS, or DOM.
How: If your UI tests from the previous release have issues, see this knowledge article, which includes steps and a custom tool to help you fix them.