Lots of advice but none seems to have a basis in law and how this will play out in reality. You have an employment contract and rights. Your co-founder cannot

Lots of advice but none seems to have a basis in law and how this will play out in reality. You have an employment contract and rights. Your co-founder cannot fire you without cause (in most legal systems). Continue working and fulfilling your duties. Document everything and all conversions with dates and times. It's unlikely you can be forcibly removed as your co-operation will be required to ensure the product continues to operate. If you are forced out you'll have to present evidence to a court or employment tribunal so proceed with this in mind. You should start off with negotiating for your full 40% share, but accept 20%. Reverse vesting a non-issue if you are unlawfully terminated. However I suspect there is more going on here as very unusual to see this kind of dispute (smoke) without cause (fire).