Names that do not match
Names that do not match are the most common stop. Invoice, packing list, bill of lading or waybill, certificate of origin and LC must use the same company names, addresses and product descriptions, within the tolerance the LC or the customs form allows. A trading style on one document and a legal name on another is enough to hold a file.
HS codes guessed too late
HS codes that were guessed at the RFQ stage show up again at export and import. If classification was never agreed, duty, licensing and sometimes the right to ship all sit on an unstable base. Classification belongs at the start of the file, not at the port.
Certificates for a different lot
Certificates that describe a different lot than the one loaded are worse than missing certificates. A COA or mill test must be reconcilable to marks, batch numbers or bill of lading references. Buyers who accept 'typical spec' certificates have little to stand on in a quality claim.
Destination documents with lead times
Destination documents are often forgotten until the vessel is booked: phytosanitary certificates, legalisation, specific origin forms, or inspection endorsements. Those have lead times. They should be listed in the RFQ and in the contract, not discovered by the forwarder.
Letters of credit that cannot be performed
Amendments under an LC are expensive and slow. If the commercial documents cannot be issued as the LC is drafted, the LC should be changed before load, not after. That is a documentation problem, not a shipping problem.
Keep a simple rule: every certificate on the file should answer a question the destination or the contract will actually ask. Extra paper that contradicts the invoice helps no one.