Failed to verify any APK from Repository

I have created a F-Droid repository on GitHub using this Docker Image, i can see the APK's for the repository on the F-Droid Android app (once repo added) but when i attempt to 'install' any of the APK's it fails with the message:-

Error installing <app name>
<path to apk copied locally by F-Droid app> failed to verify!

The procedure i used to create the repo is as follows:-

docker run --rm -u $(id -u):$(id -g) -v $(pwd):/repo registry.gitlab.com/fdroid/docker-executable-fdroidserver:master init
<copy precompiled apk's to \repo>
docker run --rm -u $(id -u):$(id -g) -v $(pwd):/repo registry.gitlab.com/fdroid/docker-executable-fdroidserver:master update --create-metadata
<commit and push to github>

So i'm obviously missing something here, do i need to somehow re-sign the apk's (3rd party apk's NOT built by me) in order for them to correctly verify?, i THINK the repository is signed ok so i'm assuming the issue is with the APK's right?, any help would be very much appreciated as i've spent waaaay too long on this.

EDIT - One other thing to note, not sure if it's relevant or not but the APK's are quite large and thus are being uploaded to Git LFS, could this be causing the verification failure?.