Index: src/wp-includes/class-wp-fatal-error-handler.php
===================================================================
--- src/wp-includes/class-wp-fatal-error-handler.php	(revision 3a229d0b477a47edf5235f6ad49f5e132ac37049)
+++ src/wp-includes/class-wp-fatal-error-handler.php	(date 1587924844254)
@@ -30,6 +30,11 @@
 			return;
 		}
 
+		// Do not trigger the fatal error handler while upgrades are being installed.
+		if ( wp_in_maintenance_mode() ) {
+			return;
+		}
+
 		try {
 			// Bail if no error found.
 			$error = $this->detect_error();