https://civicrm.stackexchange.com/questions/37277/paypal-standard-payments-are-being-accepted-but-marked-as-incomplete-transaction/37279#37279
shows how unhelpful this error is - getting data from the exception should help.
Targetting 5.28 in case the gitlab relates to a regression & we need to solicit more debug info
catch (CRM_Core_Exception $e) {
Civi::log()->error('ipn_payment_callback_exception', [
'context' => [
- 'backtrace' => CRM_Core_Error::formatBacktrace(debug_backtrace()),
+ 'backtrace' => $e->getTraceAsString(),
+ 'message' => $e->getMessage(),
],
]);
}