There is a known bug in Prokka where there is no whitespace between the contig names and the sequence length.
See: https://github.com/tseemann/prokka/issues/661 and https://github.com/tseemann/prokka/issues/337
To fix this issue and allow these files to import you will need to manually correct the missing space.
Example:
LOCUS w.thymelicus_acteon.SP_TA_344_1664073 bp DNA linear
to
LOCUS w.thymelicus_acteon.SP_TA_344_1 664073 bp DNA linear