I just wanted to demonstrate that if a population is missing from historical records for a while, this isn't a proof that population didn't exist, especially as sources are very scarce for the period. We have a gap in historical records for Romanians, it's true, but I showed you a similar gap for Aromanians too. And Aromanians lived in a much civilised zone, still Byzantines ignore them untill Vlachs start to bother them.
Actualy they deserted the cities and forts, Naissus the center of Romanic populations South of Danube is the best example. Aromanians changed from a sedentarised rural and urban population to a mostly highland pastoral one.
Those chronicles just present examples of chieftans and their retinue moving to a domain, they can't explain this
Beside this the founding of Wallachia and Moldavia was in the same way, some feudals moved with their retinue over the mountains, still they settled amongst other Romanians.
Porolissum is atested to have a continuum population untill late. We have in 200 AD a Romanic population in Dacia then without any mention of large migration we have a Romanic population in the same place a millenium later, occupying very solidly the territory as they were there since ever. Beside that there are scarce mentions to what could be Vlachs in the intermediate period, like the mention of Blakumen by Vikings.
Many Vlachs South of Danube were assimilated by Slavs. As for the chronicles, the one of Stoica Ludescu says apparently in a very ahistorical way about the origin of Romanians, being from Romans and then describing the conquest of Dacia as the author imagines it without any historic context. See also the theory of
ad migration, an intermediate one, advocating for some migration from South of Danube enforcing the already Romanic populations North of Danube. Remember also that initially Lower Danube wasn't a border as it's now between Romanians and South Slavs, but there was a continous Latin population South and North of Danube before the settlement of Slavs and under pressure from South Slavs is possible some Vlachs moved North to live amongst their people there. The ping pong theiry with Daco-Romans moving South of Danube then movign back to Transylvania is a bit streched out.