Today while doing the analysis of existing system in New Form Rendering, we realized that the SetValue function used on onChange of an attribute was in turn triggering the onChange event for that field.
We basically had an option set field whose value we were setting based on certain condition on onChange event of the same field. This was working fine in Legacy Form Rendering and also in vanilla instance of Dynamics 365.
Only in new form rendering we were getting this issue of infinite loop.
I see the similar issue discussed in the forum
https://community.dynamics.com/crm/f/117/t/165954
We are planning to raise a product support ticket for the same. Let us see what solution the product team will come up with.
Hope it helps..
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Nishant Rana's Weblog 
If lookup attribute was assigned with JavaScript with a GUID value that misses curly braces and not written in uppercase, CRM will run validation for this field once again. Make sure that curly braces {} are included value is in uppercase {XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX}.
Refer the link.
https://crmideas.dynamics.com/ideas/dynamics-crm/2527691
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Thanks Vinoth for sharing this.
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BTW the workaround was to implement the same in OnSave event.
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Hi Nishant,
Did microsoft come back with any details on this?, We are having similar issue in D365
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