Are residues from seasoning coating harmful when using carbon steel pan?
Just a note that if you use flax seed oil to season, it is notorious for flaking later. Also you may be seasoning with too much fat/oil when you heat it to create the polymerized surface.

The way to season carbon steel, woks, and cast iron is to wipe oil in the pan then wipe it out so that you can barely see a sheen of remaining oil. THEN heat it to the smoke point and let it fully dry and repeat, repeat, repeat! Again, when you first put in the oil/fat, you MUST wipe it out. That will allow for the polymerization to work as intended and not leave a surplus, sticky, or exessive quantity that doesn't complete polymerization with the pan in full.

Bon appetit!