Understood. This is then an issue of "rounding" tolerance which is apparently more strict with zenphoto than with other software.

If I see right the shutterspeed value is processed in line 438-447 of /zp-core/exif.php. The comment speaks of the value possibly being in APEX mode. Whatever that is.

any help on how to resolve this ?

You could experiment with the lines I cited above but otherwise currently no idea. Sorry.

found a problem.
somewhat exiftools read "Exposure Time" wrong. but "ShutterSpeedValue" is correct.

can you guide what changes would require so as it reads ShutterSpeedVlue not exposure value?

Have you tried to disable that meta data field on the options (if it exists, haven't looked)?

Well I think there is only one option available and its shutter speed option in zenphoto admin

Then this probably requires more investigation …