Is there any newsletter informing about new versions of Core?
There is no newsletter. One can monitor https://www.support.xerox.com/support/core/downloads/enus.html?operatingSystem=win7 to see if there is a FFCore update.
Is this BUG with collect node are fixed in 5.4.4?
The problem "Job going through one branch of Split node getting stuck in the Join node" you described (earlier in this thread) with the Join node was fixed in 5.4.3. I assume this is the problem that is being referred to.
OK, 5.4.4 helps for not working Join node