I have a custom taxonomy that has some ACF fields (Description and featured image). When I create a template for this taxonomy everything works until there is a post assigned to the taxonomy term.
Step-by-step reproduction instructions:
Create a custom taxonomy
create an ACF for the taxonomy (e.g. image)
create a term and select an image for the term (do not assign any post to this term yet)
create a template for the taxonomy and use the ACF image
preview the page of the taxonomy term you just created. It should work as expected
Looking at this a bit more closely, it doesn’t seem as if you set a location for the ACF Field, which will inevitably fall onto a post ID when necessary.
A Taxonomy Terms block would have been necessary as it allows to be used as a location parameter in the dynamic selector.
In 1.2.9.5.7, we have added a new property Current Taxonomy Archive that allows you to achieve the same result without the Taxonomy Terms block.