Problem statement
We are aware of an issue that seems to have begun on September 3, 2024, where in SharePoint Online, Microsoft has switched custom lists to a new user experience, which is causing custom list actions you have created with Lightning Tools Actions to no longer appear. This only applies to actions that should appear when one or more items have been selected.
Investigation
Please see this GitHub issue: onListViewUpdated() method not firing for SPFx CommandSets on Modern Page · Issue #9898 · SharePoint/sp-dev-docs (github.com)
This GitHub issue also appears to be related: The new Microsoft Lists layout on SharePoint lists breaks ListView Command Sets, selectedRows is empty. · Issue #9907 · SharePoint/sp-dev-docs (github.com)
The issue with Lightning Tools Actions on selected items appears to be related to a function that has been suddenly discontinued by Microsoft.
Sept 5: Our developers have been able to identify a way to resolve this issue. We are working with urgency on an update to Lightning Tools Actions.
Resolution
As of September 6, Microsoft has rolled back this update, so your custom list actions should now be visible again. Our developers have found a way to handle this if Microsoft pushes out this update again, so this will be part of our next Lightning Tools Actions release.