Beginning to send out newsletters - newbie questions

Your software
My Mautic version is: 4.4.10
My PHP version is: 7.4.30
My Database type and version is: mysql / 5.7.25

Your problem
My problem is:

I am starting to send out newsletters with my self hosted Mautic installation.

So far so good, it works… somehow.

When sending out the newsletter I will be asked if I would like to send out in batches. Fine for me, my contact list is about 600, so I decide do do batches of 100. Mautic will send out 200 e-mails and then stop without any error. The status bar does not grow it still says “0 out of 600” sent. When duplicating the tab it will say that 200 e-mails have been sent out and 400 are left. So I press “send” again. Also the status bar does not grow, I see that they are sent out (via my E-mail tool).

I use Gmail to send out the e-mails. Is there any restriction or delay in getting back the information of how much was sent out?

With the first newsletter sent out I also got a few “address not valid, bla bla bla” messages in my inbox. I sorted them out manually for the time being.
Is there any way to use another way to sort this out (using the reports or something?)

I just checked the error log and it gives me tons of lines of this error:
[2024-01-04 06:16:13] mautic.ERROR: Invalid clickthrough value: Yjo4OntmOjk6ImZiaGVkZiI7Yjo1Ont2OjM7Zjo4OiJmemJ2eSI7djo0O3Y6NDg7fWY6ODoiZnpidnkiO3Y6NDg7Zjo3OiJmZ2JnIjtmOjU1OiI5ODI5N2U0MWRlNjk4NDU0MDA3MzY4IjtmOjc6InlmYmUiO2Y6NjoiNzUyIjtmOjA6ImR1YmFhZnkiO2I6NDp7Zjo4OiJmemJ2eSI7djo0ODt9fQ== {“exception”:“[object] (Mautic\CoreBundle\Exception\InvalidDecodedStringException(code: 0): The string b:8:{f:9:"fbhedf";b:5:{v:3;f:8:"fzbvy";v:4;v:48;}f:8:"fzbvy";v:48;f:7:"fgbg";f:55:"98297e41de698454007368";f:7:"yfbe";f:6:"752";f:0:"dubaafy";b:4:{f:8:"fzbvy";v:48;}} is not a serialized array at /var/www/web27928423/html/XXXXX/mautic/app/bundles/CoreBundle/Helper/ClickthroughHelper.php:37)”} {“hostname”:“alfa3206”,“pid”:3421000}

I guess this is just a configuration thing with Gmail but I don´t know how to solve it.

Thanks in advance,