Here is my Theory... When the first filter is removed from the D35 projector, that essentially doubles the output of UV light which is why we have to instantly drop the MSM of the machine down to around .500 and slowly work our way up if needed.
There is a second filter inside the casing that is not part of the removable lamp assembly.
I suspect that if you use the modified projector with a high MSM number 1 or 2 times without an additional fan , that the second filter will crack. That will allow extra heat into the lense area where there is a heat sensor . That cracked filter, combined with the heat sensor will shut down the projector . Attaching a picture of the cracked filter within the casing.
Please take a look and see if this filter is cracked... if it is, then , replacing this and putting an extra fan on your projector may help the longevity of this part.
I am not sure that this is the problem, but I strongly suspect it.