With the New DQA:

• Evidence related to a single subject
  

This project is now redundant.

All southern African observations from the project have been checked are marked as

• Evidence related to a single subject FALSE
  
  (except those that have been fixed, which are marked as TRUE).
  and the instructions added where they had not been done previously.

Please do so for your region, and we can park the project. Although it is here if anyone wants to highlight something or add an observation for future checking.

At this stage it is not possible to filter observations for DQA: Evidence related to a single subject

• But for most of the southern African observations this workaround finds most of them:
  https://www.inaturalist.org/comments?q=discombobulate
  (but this includes those that have been fixed).
  

Links for dealing with multiple species per observation

https://forum.inaturalist.org/t/how-to-fix-your-observation-with-photos-of-multiple-species/15096
&
https://forum.inaturalist.org/t/como-arreglar-tus-observaciones-con-fotos-de-multiples-especies/24540
https://www.inaturalist.org/posts/49611-duplicando-observacoes-ou-separando-uma-com-multiplos-organismos

Multiple species per observation.
Sorry! iNaturalist takes only one species per observation. Please split these species into different observations. You are allowed multiple pictures per observation, if they are of the same organism at the same place and the same time.

So please discombobulate this observation. And then when you are done delete it (or you can keep it for the first species, if you edit and remove (untick) the other observations.
If you are using the web version, you can "duplicate" the observation (click the v on EditV top right), and untick the pictures you dont want and then save. Dont untick any from this observation until you are done, otherwise any pictures will be deleted if they are not connected to an observation.