Intel isn't only struggling with a naming scheme that no one can understand, let alone pronounce; due to Coronavirus/Covid19, a massive number of tech production facilities have been shut down either partially or completely.
Unikoshardware has come in possession of images of not only the upcoming i5-10400, but also an internal slide that speaks of a "Press News Embargo: April 13 - June 26, 2020", and a confidentiality notice. This indicates that the original release date that was rumoured to be somewhere in April or May was true, but most likely has been pushed to June 26.
While the main Intel CPU factory currently remains unaffected by Coronovirus as far as Gamereactor is aware, it makes sense to delay the release as most likely every single motherboard partner in the industry is having problems with both supply chains and production.
The dates indicate the expected reveal of the chip to be April 13, with a retail release on June 26. It could also indicate that different chips have different release dates, with the last one being June 26. We'll just have to wait and see.
<bild>Image credit: Unnikoshardware.com</bild>