A suitable product contact material is necessary, but it is not the whole hygienic design. Product can remain in poorly cleaned spaces around a seal, and the seal can wear or leak in service. A certificate for the elastomer does not prove that the assembled seal and its housing can be cleaned in place.
Look at the full wetted design: where product sits, how the faces and secondary seals are exposed to cleaning fluid, and whether the equipment can drain as intended. Check the cleaning and sterilising sequence for the installed assembly, not just the separate seal part. The EHEDG guidance on hygienic and aseptic mechanical seals and elastomeric seals is useful here, but a claim that a design follows guidance is not the same as certification of a particular assembly.
If you have a repeat contamination concern, preserve the failed components and involve QA and the equipment team. I would review the seal, housing and cleaning duty together rather than simply changing the O ring grade.
Andrew Sykes | Acumen Seals & Pumps Limited | Independent mechanical seals and sealing specialist