The following is the manufacturer's warranty policy as published by Optolong.
Optolong Warranty
Optolong Filters Warranty
All Optolong filters are strictly inspected within specifications before shipment. Each filter will arrive clean and well packaged in an anti-counterfeiting code.
Mechanical function and optical performance of all Optolong filters could always be guaranteed for 3-year under normal use. This warranty is void if the filter has been misused or damaged.
We would like to offer you a technical support or official direct if need. We will also provide assistance in dealing with your issues if happened during imaging or application.
Kindly email us at contact@optolong.com, and let us know more details. We would like deal with your problems immediately as soon as we receipt of your message.
Source: https://www.optolong.com/cms/document/detail/id/149.html