There is disagreement as to whether Jin Chinese should be considered it's own dialect group, or rather a cluster of similar Mandarin dialects. From wikipedia:

Until the 1980s, Jin was universally considered to be a dialect of Mandarin Chinese. In 1985, however, Li Rong proposed that Jin should be considered a separate top-level grouping, similar to Cantonese or Wu Chinese (that is, its own dialect group). His main criterion was that Jin dialects had preserved the entering tone as a separate category, still marked with a glottal stop as in the Wu dialects, but distinct in this respect from the other Mandarin dialects.

Oher linguists have subsequently adopted this classification. However, some linguists still do not agree that Jin should be considered a separate dialect group for these reasons:

Languages and dialect groups are not normally delineated based on a single feature but rather on a cluster of features distinguishing the group from other related varieties as well as mutual intelligibility. Use of a single diagnostic feature is inconsistent with the way that all other Chinese dialect groups have been delineated.

Certain other Mandarin dialects also preserve the glottal stop, especially the Jianghuai dialects, and so far, no linguist has claimed that these dialects should also be split from Mandarin."