If you refresh your NetSuite sandbox, your Kolleno sandbox will always need to be re-synced. NetSuite regenerates every record's internal ID during a refresh, so Kolleno's stored IDs no longer match.
As a result:
New records that look identical to old ones will be created as duplicates.
PDFs and other data for previously imported records can no longer be fetched.
Updates between the two systems stop reconciling correctly.
Fix: contact Kolleno Support to wipe the existing Kolleno sandbox data first, then re-synchronize against your refreshed NetSuite sandbox. This only affects sandbox environments; production is unaffected.