looking at my mail logs, some emails get through but there's a spamassassin timeout (it seems) and the sender receives an error message

From the logs (with some redactions):

{
  "ts": 1654119816747,
  "type": "denied",
  "direction": "inbound",
  "uuid": "90D87FE5-8626-4CBA-93BA-94B8ED1FD2A0.1",
  "messageId": "<[REDACTED] D053D0638D20@gmx.net>",
  "mailFrom": "<[REDACTED]@gmx.net>",
  "spamStatus": null,
  "rcptTo": [
    "<[REDACTED]@[REDACTED].net>"
  ],
  "remote": {
    "ip": "[REDACTED]",
    "port": 39538,
    "host": "[REDACTED]",
    "info": "[REDACTED]",
    "closed": false,
    "is_private": false,
    "is_local": false
  },
  "authUser": null,
  "relaying": false,
  "pluginName": "spamassassin",
  "errorCode": 903,
  "message": "plugin timeout",
  "rejectionCountLastHour": 0
}

Anything I can do to mitigate this?

Mail has a 4 GB memory limit and there are 2 DSNBL zones activated:

bl.mailspike.net
noptr.spamrats.com