Response from Privium below, bolding is mine:
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Dear Ana,
Thank you very much for your email about the queues at Schiphol Airport. I am sorry to hear that you had a negative experience. It is understandable that you would like some more information about this. I am happy to help you further.
Short of a technical outage, the Privium gates should be readily accessible. I trust that this was a one off outage and during your next visit you will be able to access through the Privium gates. You can also approach the Schiphol staff at location to check why the gates are not available.
Your Privium membership gives you priority access over the regular passengers. In some cases it can be that the fast track lanes will merge with other Priority passengers. Premium passengers and Privium members exit to the security check via the priority waiting area, and will reach the security check much faster than regular passengers. There are no passages at the actual security check that will separate Priority passengers from Privium passengers. I hope this has clarified the process at security. We appreciate your loyalty and will take your feedback to adjust and improve our services.
If you have any further questions, please do not hesitate to contact me again. I wish you a pleasant day.