Normally, split returns the bits either side of the delimiter, but not the delimiter itself. You've overridden that behaviour by adding capturing parens around the delimiter. Hence, it treats your input string as consisting of a sequence of null strings separated by 6 character delimiters which you've also asked it to capture:

(null)df5434(null)vg7856(null)fg3472(null)sd1234(null)jh45r5";
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Basically, you're using the wrong tool for the job. m// does what you want:

print for "df5434vg7856fg3472sd1234jh45r5" =~ m[(\w{2}.{4})]g;;
df5434
vg7856
fg3472
sd1234
jh45r5
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But actually, the most efficient way of breaking a string into fixed length fields is unpack:

print for unpack '(a6)*', "df5434vg7856fg3472sd1234jh45r5";;
df5434
vg7856
fg3472
sd1234
jh45r5
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