I don't think I changed anything in how the model importing code works recently...
You have any more information for me?
Working with this on 4.26 I am also having extreme memory usage issues when importing materials to the point that unreal crashes as it runs out of memory (64GB+ of RAM & 100GB+ Pagefile Size) when doing imports - typically at the "creating materials" stage. Running the same import on previous versions does not seem to cause this issue, possible memory leak?