Grading criteria changed mid-semester. Not fully communicated. What can I do? I'm in my final year of my bachelor degree (Netherlands). In fact, I am resitting this particular class since I did not submit the portfolio last time. I have agreed to start writing my thesis today in collaberation with a business on the condition that I would receive a pass grade on the portfolio for this class that was due two weeks ago. I submitted it, fully following grading criteria that I found in the syllabus. Last Friday I would receive my grade. 

I received 43/100. I needed 55/100 to pass. The grading criteria were very different from the criteria mentioned in the syllabus. In particular not a single word was mentioned in the syllabus about a certain chapter required in the portfolio worth 20. I and various other students missed that part.

It turns out the syllabus change was communicated in an extra class that I was not aware of. This class was not visible in my agenda. It was not uploaded to the Blackboard environment nor communicated by e-mail. The extra class was recorded and a link to the video was posted in a Slack environment that is not official. 

I would be allowed to resubmit the portfolio 8 weeks from now, be graded 2 weeks later and then start writing my thesis. The professor (who realized the communication on this was poor) allows me to resubmit the portfolio as soon as possible instead

Meanwhile, I had to communicate this change to the company I would be collaberating with. They are, understandably, not happy. Moreover, this change requires me to enroll an extra semester and as such is quite a big financial burden on me.

What can I do? Can I appeal? If so, to whom? Will appealing be able to change anything? Depending on when I can possibly start my thesis, I may not be able to finish before the two-yearly thesis defence.
You can try, of course, the question of who to depends on your university. I would start with a student advisor for your subject and take it from there. If you combine your efforts with the other students who also have trouble because of that change right now, that might help.
Furthermore, you should not start with officially appealing right away, as this might force people to take a defensive position against you. I would rather explain the situation, the problems that it causes you, etc. and ask the advisor for a solution.
If you formally appeal and try to get a passing grade through that, that might or might not work. But it will surely burn some bridges and, even worse for you, the whole process will take even more time than writing the missing chapter would.