Syslog processor more strict than syslog input


I'm trying to gather logs from Netgear switches using Syslog.
The idea is to configure all the switches to send logs via Syslog to a single filebeat instance and this filebeat instance is then sending the logs to an Elasticsearch instance.

I've been able fairly easily to achieve this setup with a syslog input configuration but I've seen in the documentation that Syslog input is deprecated and must be replaced by UDP input / Syslog processor.

The problem is that my message is not correctly parsed by Syslog processor.

For this syslog message:
<14> Jun 27 12:00:32 General[-1248711972]: <mark>main_login.c</mark>(763) 1771 %% HTTP Session 5 initiated for connection from

I have this error.message:
syslog failed to process field "message": parsing error at position 5: unexpected EOF

The same message is correctly parsed by syslog input.

Do you have any ideas on this problem ?