Bulk Management - CSV upload processing delay



We've been using CSV upload feature in Bulk Management very often. The processing was usually so fast that it was completed in a few seconds.

However, it took more than 2 hours yesterday.
(We didn't have internet connection issue at all, and we uploaded only 44 asset informations yesterday)

but today it was completed as fast as usual speed again.

I'd like to know the factors that can affect the speed of CSV upload.