There should be no problem with running multiple custom promotions at the same time. it sounds like your site has a problem with content model sync. Did you contact developer support service?
It not only occured on DXC but also occurred on my local. I mean i am able to reproduce on my local. So i don't think site has a problem with content model sync
I even delete all promotions related to those custom promotions and i also delete custom promotion type in table [tableContentType] in order to init its again. But issue still occurs
In your SetDefaultValues() method you've specified a redemption limit:
RedemptionLimits.PerOrderForm = 1;
Is this the problem?
I create two custom promotions but i don't why each time i recycle app pool all promotions not work, if i publish promotion again and it work again
I try to disable one of the two custom promotion => every thing work fine
So, Is it possible that when running two custom promotions at the same time, they conflict?