This may be about the coordinate system the html annotation uses to recognize the linked feature.
I've had the same problem for awhile. I decided to start from scratch and create a new, very basic QGIS project and try to get HTML annotations to work with it. To my surprise they did, so I compared the working QGIS project to my old one in a text editor. I noticed some lines in the HtmlAnnotationItem block were different...
<HtmlAnnotationItem hasFeature="0" feature="0"
<HtmlAnnotationItem hasFeature="1" feature="52196"
In both cases I had added the html annotation in the same way, making sure to have the layer selected in the layer panel when I did so. I tried editing the original file to look like the other by putting hasFeature=”1” and feature=”52196”----which is just the feature ID of where I had put the annotation. That didn't work.
Another discrepancy in the HtmlAnnotationItem block was…
I’m not sure what the srsid is, but the srid I recognize as being the geographic and projected coordinate systems I use. The new project I created defaulted to the srid of the first layer I added, which was 4267.
My feature layer in QGIS is a postgis view where the geometry srid is 4267, in QGIS I have it transformed ‘on the fly’ to 26714. I edited my view in postgis to transform my geometry to 26714, and html annotations now work fine. Apparently the annotation was trying to use the project coordinate system to link features but was not connecting to underlying view in this case, because it had a different srid and thus different coordinates. I noticed your project was srid 26710, if the datasets you were using are in a geographic coordinate system I think our problems were probably the same.