I'm 99.99% sure that there have been essentially constant contact between Siberia and Alaska since humans first arrived. The distances are easily traversable using the watercraft of the Americans and Asians.

Not sure if they conveyed 'civilization' with them per se, but there does seem to be a material continuation in the region.

I suspect the establishment archeologists don't like to admit this because the hyper isolation aspect helps bolster their narrative regarding the European colonization narratives - especially the idea of native depopulation based on immune systems were not capable of handling old world viruses as opposed to major economic devestations intentionally inflicted in order to facilitate land theft.