First of all, correct, who leads the non-restrictive attributive clause to be preceded by a comma,

Then he met Mary who invited him to a party.

Later he met Mary, who invited him to the party.

Because the special case in this sentence is parentheses, it is separated by commas. Adding a comma after who was not intentional. Please delete "under special circumstances" and look at this sentence:

Zhang Pingyu found that the Queen's jewels were protected by special royal soldiers, who still wore uniforms with a history of 400 years in the era of Queen Elizabeth.

Zhang Yuping found that the Queen's jewels were protected by the Royal Special Guard, who still wore 400-year-old Elizabethan uniforms.

With the brackets on special scenarios, the meaning of the sentence remains the same, except "on special scenarios".

Zhang Yuping found that the Queen's jewels were protected by the Royal Special Guard. They still wore 400-year-old Elizabethan uniforms, which were only worn on special occasions.