After upgrade ros to 7.6 on CRS305 cpu increased from 1 to 2 cpu wtf ? 
RouterOS is very powerful system and v7 is especially good. And rumour is that v8 might be even better and add two more CPUs! Yay!
Ok, I’m kidding, it’s either that one CPU was disabled in v6 for some reason, or it’s some display bug, but I’m not sure which one it is. I didn’t pay much attention, because I don’t have such device. But use search and you should probably find it.
Probably same issue that CRS328-24P-4S+RM had.
https://forum.mikrotik.com/viewtopic.php?p=939191&hilit=3236#p939191
Expect problems.
The crs3xx series (many of them) have arm cpus. Many of the cpus have multiple cores, but with the older kernel could only use one with ros 6. With ros 7, these extra cores were enabled due to the newer Linux kernel. The crs328 is the only device so far that has had the extra core disabled in ros7.
Hi!
I did not notice the change until reading this post, but on my CRS305, now running 7.7beta4, I have 2 cores as well.
This looks similar like on IBM mainframes, more cores can be enabled by SW. Except: IBM will ask you something in reverse…
OR maybe this is the remedy for the unavailable RB5009s, for every further quarter missed, we get one additional core… 
Bad jokes aside:
I did not experience any issues until now, but I only have a simple “switch with VLANs” config. No routing, nothing else fancy, almost everything left at default.
And I ran that switch only for a few hours, but copying a lot of files to a NAS over it.