Post update the Lab in Stronghold is only showing one “ongoing” research item for those with a lab level capable or researching more than one item at once.
It is possible to start the multiple items, but only the first one started is visible in the ongoing research - completing further items requires finding them under “all research” and hitting the complete button there.
It does appear to be completely visual UI related.
Guys, found a way around this UI bug for anyone that isn’t able to research 2 things at a time.
Open your lab, change “Available Research” to “All Research” and just scroll until you find the one you completed and start another one, this way you can have 2 at a time.