Apache2 not serving images from n/w share

I have three web servers at home all running Apache2, one is a new build but it is not serving images from a network share:

1] Apache/2.4.25 (Raspbian) serves local images and images on the network share
2] Apache/2.4.38 (Raspbian) also serves local images and images on the network share

3] brand new image built 2-Oct-2020:
Apache/2.4.38 (Raspbian) also serves local images and images copied from the network share to a local folder but this build does not display images from the network share.

The network share is the same in all cases with the same user permissions, the html [actually php] is the same in all cases. The php reads in a list of the images in the folder to get the file names of the jpgs to be able to display them via <img src=... /> it gets a list of the file names from the network share but fails to get the content of the actual images.

If I browse directly to the image: http://192.168.1.4/Web-Cam/Hill/Main...0-snapshot.jpg when the image is in a local copy of the folder it works, if the image is in a network share I see the following text:

The image "http://192.168.136.4/Web-Cam/Hill/Main-20200927-111000-snapshot.jpg" cannot be displayed because it contains errors.

the folders containing the images are all mode: 755 and the images themselves are 644

apache2.conf is the same on all builds and is unedited, same with php.conf

I have rebuilt the build three times, just in case I did something daft, it was the same in each build

in the error.log in the machine that fails, I see:

Content-Type 'image/jpeg' ...
... did not match 'application/xml'

for a whole bunch of things that it did not match

I am quite perplexed and I am sure it is something simple that I have missed