I am unable to open attachments in ArcPro for feature classes that have attachments or for hosted feature layers that have attachments.
I can open the map in AGOL or the hosted feature layer in AGOL and see the attachments. No issue opening the same attachments on a different computer.
Any chance you are clicking on either a feature with more than one attachement, OR, close enough that you are clicking more than one feature with attachments?
Pro 2.9.4 and later have a bug with HFLs where you are not able to do the above. It will only allow you to click on a single feature with a single attachment, or it throws error.
If you select the feature(s), are you able to see/access the attachments in the attributes pane?
R_
I am experiencing the same behavior with Pro 3.2.1 with feature class in our SQL Server enterprise geodatabase . I hope that this is fixed in the latest version!