Half reading the source code I suspect it has something to do with
using a "; %1 fps" formatting string instead of "; %.1f fps" ?

My example was a fast repacking of an MXF (no JP2000 encoding) with high fps.
I noticed in other encoding runs that there is no decimal in the fps number:
for example just "7" instead of the more interesting "7.3".

It does also happen with encode jobs (not only with repacking).
When the fps gets higher than 10 it switches to "1e+01".

Thanks for the report! This should be fixed in 88e41b59802a41aaeddd17667da33532280d1e31 (main branch) and ad05b0289e6f11bb0541ec8413748e855d7add77 in v2.16.x.

These commits will appear in 2.15.181 and above.