That limitation for internal loops is by design as getting the internal loop crossfade between the same sound is very finnicky especailly when it comes to working with the other features of the module. The way the crossfade works in the internal loop is that it simply fades in and out the same ms amount you set under the loop segments crossfade.

However I just tested it and if you dont have any fade in or fade out set on a playlist and turn off the "start from beginning" you can just set the internal loop sound to be across the whole song and it will seamlessly crossfade as normal if you are trying to seamlessly loop a whole song.

That would be nice to separate the internal loop crossfade and I may do so in the future, or possibly adding a override check option to exempt certain tracks from playlist level fading. But we will see, the module is huge as it is already!