First: Welcome to the forum!
Well, as per a 2016 thread on this forum they are not the same.
Well, but they are indeed the same. Small differences maybe visible only due to some batch-to-batch variation (which can happen especially with cheaper film).
If you compare them side-by-side under identical test conditions, and if you evaluate their characteristic curves you immediately see their identical origin.
And, by the way: When this film was introduced to the market one photo chemistry manufacturer had a severe staff bottleneck and ask me to evaluate this film in their developers (generate data for the developer datasheet). So they outsourced the work to me (I am running an independent photography test lab). They shipped their developers to me for the test and the films.....Kentmere 100 and 400 (at that time the films have not yet been available in the AgfaPhoto packagings; and the chemistry manufacturer wanted to be early enough on the market with the developing data).
Kentmere 100/400 is also repackaged as Fotoimpex CHM 100/400 (Fotoimpex has always been absolutely honest on this and given their customers the Kentmere developing times), RPX 100/400, Oriental 100/400.
Both films (100/400) are solid performers with a very good price-performance ratio. One major difference to FP4+/HP5+ is the worse anti-halation layer of the Kentmeres: At light sources and highlight detail (e.g. reflecting metal) you get a kind of "halo" around the light source or reflecting detail.
Best regards,
Henning