Photos won´t launch recognizing faces (Macbook pro/Catalina)

I keep my photos library on an external HD. I have never spent much time with the app on ( just sync / backup) and then the HD out. I have noticed recently that there is no face recognition in m library at all (" 0 photos scanned"); if I click on the show album/faces he just shows 3 pictures I marked myself on manually.

For the last few days I have been trying to keep the external HD connected, with the Mac on, Photos app on (and off). I did repair the library too, which took like 3 days ( 270 Gb of pics and videos).

Nothing seems to change anything.

In the Mac activity tracking there is a certain activity of photoanalysisd ( I guess it means the library is working somehow).

The date of the last change of the photos library file seems to be stuck too, even though I have opened it since (slow as always, but works) , normally sync it with my Iphone pictures ( even today), but the date the file was last changed stays stuck on a date 2 months ago. Not sure if it is of any significance.

My photos app on the Iphone ( XS, last iOS update) seems ok with 15 recognized people but won´t launch recognizing the 16th one, not sure if it´s normal or not.

Do you have any suggestions how can I "kick" my photos on Myc or Iphone to launch recognizing faces ? Connect the external HD with the photos app off (or on ?) and wait for weeks ?

Thanks in advance, P