In cases where a JwtParser is built using b64Url() to provide a custom base64 decoder, the expectation is that all base64 decoding will use the custom decoder:

Jwts.parser()
    .verifyWith(publicKey)
    .b64Url(decoder) // expect this decoder to be used for all base64 operations of parseSignedClaims()
    .build()
    .parseSignedClaims(jwt);

However due to

This violates the expectation that the custom base64 decoder will be used for all decoding. This behavior has changed somewhere between 0.11.5 and 0.12.5 which in turn breaks our application if we update our jjwt dependency version to the latest.