Could dental xrays miss a dental abscess?

Yes.. many times. : While taking a regular dental radiograph is a routine / initial diagnostic approach for many dental problems, these traditional 2 dimensional images are not capable of exploring some dental abscesses, specially if the abscess, or infection is deeply situated inside the thickness of the jaw bone, or routinely missed palatial roots of upper teeth. A 3-d image/ cone beam ct scan can help much more.

Yes, it is possible: Dental abscess is easy to diagnose by dental/medical history, symptoms dental examination, and x-rays. In many cases only x-ray is not enough for the proper diagnosis. Dentists are well-trained to rule out dental abscess or other oral infection.

Yes: But not likely. There are also CBCT (3D) dental images that reveal ore than 2D routine X-rays.

Abscess: Yes. As toxins spread out of the root's canal(s) it takes time for the toxins to cause the surrounding bone to dissolve away and thus become visible on an x-ray.

Yes: It all depends on quality of xray; skill of xray technician; size of xray film/sensor used; positioning of the xray film/sensor; bone density/pattern and last but not the least what machine is used (intraoral xray/ extra oral hand held xray/ pano machine/ cbct)