I don't have time to submit a help request to get this logged as a bug right now, but just want to document that the data tab of the Item Details page for feature services that include multiple layers is not reloading after adding a field.
In other words, if I open the Item Details page for a hosted feature service that has multiple layers, and I select one of the layers and then click the Fields option on the left and add a new field, the page doesn't reload properly after the new field is added. I can no longer select a layer and no fields are displayed. Clicking the Table option on the left also doesn't display anything. In fact, the only way to get the data to display again is to reload the browser tab. This is annoying and inefficient when I need to add several fields to the same layer. I have experienced this with two separate feature services since the June 2025 release.
Before adding a field:

After adding a field:

Also, the data tab in general is very slow to load.
If anyone has figured out how to get around this besides reloading the tab, please share.