I put a ticket into support regarding this. I am having the same issue, with cosmetic dlc.
So far placing castle walls or funfair items causes desyncs, the game recovers but its an insufferable delay to place every piece.
I can place them in blueprint but as soon as I hit upgrade them bam desync.
When the game recovers they are placed and built.
This really needs a fix, love the game but I only play multiplayer and I love making really pretty cities.
We've managed to reproduce the issue and will have a look at what's causing the problem. We won't be able to address this with the upcoming update, but will hopefully have a fix for the next patch after that.