Wrong encoding?

Your software
My Mautic version is: 4.4.2
My PHP version is: 7.4.2
My Database type and version is: MariaDB

Your problem
I sent a mail campaign last night to 7350 contacts.
It’s a ‘marketing’ type of campaign, using ‘send emails’ as ‘actions’ → send immediately.

I am not using CRON jobs as I prefer running the command manually.

My queue settings was Screenshot by Lightshot

Despite the settings, I ran the command mautic:campaigns:update and it created 22 batches of files (checked under /var/spool) with 300 messages in them.
Q: I set 50 messages per batch as per my settings, but it actually created batched with 300 messages, which is the default settings of Mautic?

I wanted to have a semi-smooth delivery, hence I raun the command:
mautic:email:send --message-limit=100

But I noticed the limit was not respected and all of my messages were sent out in on go to my SendGrid API SMPT.

Q: where can I find the send logs ?

Finally, I checked again under /var/spool and noticed there were 7350 messages, which I presume are the logs for each message sent.
I randomly checked few logs and noticed the majority are econded in UTF-8 (Screenshot by Lightshot), which is right, but many have been printed like this:


Q: Why some logs were printed with broken charset? Do all these 7350 messages in /spool represent the ‘sent’ messages? According to SendGrip API just 300 messages were delivered.