Yes it's quite common, that's why aerospace materials specifications were written to require the material to meet cleanliness to a given requirement, and of course costs more but if cracks show up, the material can be returned for replacement. Plain old commercial quality 1018 cold roll etc, no gaurantee. If Your material was purchased to ASTM A1018 or UNS G10180 it should be returnable.
Causes, various, most cold finished bars are produced by cold drawing, oversize hot rolled bars are drawn through dies to the required size, improper cleaning will cause inclutions, if the material has been drawn down a long way will cause longitudinal cracks as You decribe.
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