Hi @Ede,
this is a complex problem. So I first think you lost your data because you have no volume to persist your data. Every container has his data only as long as it is running, imaging this as a sort of tmpfs. If you now use your old image this will be also empty because your container was “destroyed” during the update and that is the point when you loose your data.
So I would recommend you to first create a persistent volume for your data, follow this guide to bring the volume to the right point inside the container. For any further updates you have to follow my last link about the update procedure.
To be sure about your data you could open a shell inside the container and check /omd/sites/YOURSITE and try this with the older images. If you have some files there with your current container, than you “only” need the update procedure for CheckMK.
I hope you understand my thoughts.