After the USX derailment, @solsticefi updated the reserve certificate, which appears to be normal. The certificate was provided by a third party, @AccountableData.
AccountableData is an independent third-party organization that has issued POR certificates for approximately $2 billion. Besides Solstice, other clients include @Neutrl and @MuDigitalHQ.
Personally, I feel Accountable is more trustworthy, at least more reliable than getting a letter from some random Hong Kong accounting firm.