Recently I faced issues with some of our custom and Out of the Box ribbon buttons disappearing for example look at the snapshot below.
For any selected service order I was not able to see the Run Flow button which runs on-demand workflows and Power Automate Flow (and a few custom ribbon buttons as well).
I investigated and found out that this happens because of a field service setting called “Show Simplified Work Order Command”.
As per the document – https://learn.microsoft.com/en-us/dynamics365/field-service/configure-default-settings
This setting influences the command bar on work order records and lists. By default, this field is set to Yes, which shows only the most relevant commands for work orders. The following commands will be hidden from the form: deactivate, check access, process, add to queue, queue item details, assign, share, email a link, flow, Word templates. The following commands will be hidden from the list view when no records are selected: email a link, flow, import from Excel. The following commands will be hidden from the list view when a record is selected: activate, deactivate, email a link, add to queue, flow, Word templates, Excel templates. When set to No, all commands are shown.
To turn it off in your field service app go to settings from the change area and select Field Service Settings, under field service setting turn off Show Simplified Work Order Commands to No.
Now we can see our run flow button along with a couple of other buttons.
I hope this helps!