Names of places in Croatia

[FlatAssembler]

So, a forum.hr user called DarkDivider claims that Proto-Slavic phonotactics didn't allow four syllables with yers to be consecutive. If true, that would make my etymology that Karašica comes from Illyrian *Kurrurrissia (via a Proto-Slavic form *Kъrъrьsьja) invalid, as *Kъrъrьsьja contains four consecutive syllables with yers. But I cannot find any reliable source claiming that or claiming the opposite. I have asked that question on Linguistics StackExchange and have started a bounty, thus far to no avail. It sounds like a weird claim to me because phonotacticses of various languages usually do the opposite (requiring vowel harmony...).