certificate not trusted

Hi.

I use Google Translate because I can't English.

I'm sorry if I do not understand the sentences I wrote...

Push notification service is implemented by Node.js.

From 2018/04/24(UTC), I occasionally get an error saying "certificate can not be trusted" when connecting to APNs. Currently not happening.

This is the log when the event occurred.

[2018-04-25 05:50:21.046] [ERROR] [2532] - MSG:531525[2] | Error occurd send APNs: { [Error: certificate not trusted]
  stack: 'Error: certificate not trusted\n    at Error (native)\n    at TLSSocket.<anonymous> (_tls_wrap.js:906:36)\n    at TLSSocket.EventEmitter.emit (events.js:104:17)\n    at TLSSocket._finishInit (_tls_wrap.js:457:8)',
  code: 'CERT_UNTRUSTED' }
Error: certificate not trusted
    at Error (native)
    at TLSSocket.<anonymous> (_tls_wrap.js:906:36)
    at TLSSocket.EventEmitter.emit (events.js:104:17)
    at TLSSocket._finishInit (_tls_wrap.js:457:8)

I changed the certificate but it still did not work

I have not changed the web application recently.

• Please tell me why this error occurs and if there is a way to avoid something if this error occurs.
• Have you updated or changed APNs near April 24, 2018?