Invalid claims: iat not parsed correctly?

We are using Shinyproxy with Open ID configuration. However, we constantly got errors when Shinyproxy tried to parse the iat value in the claim. The iat is simply sent as the Unix Epoch Time (millisec since 1970):

long iatMillis = 1658769280 ; //Mon Jul 25 2022 17:14:40 GMT+0000

However, Shinyproxy parsed it into a non-sensual value like “+54540-04-15T13:38:35Z” (see below). Can anyone here help? We have been stuck with this for a week. Thanks!

Jul 27 16:41:08 shinyproxy java: 2022-07-27 16:41:08.732 ERROR 28634 — [ XNIO-1 task-1] e.o.c.a.i.OpenIDAuthenticationBackend : [invalid_id_token] An error occurred while attempting to decode the Jwt: The ID Token contains invalid claims: {iat=+54540-04-15T13:38:35Z}