I'm sorry if this is not the place to put things like this, but i thought you might want to know, so you had a chance to improve in the future :)
We started using TeamCity in 2015 and was actually pretty happy with it, until about a year ago.
As we started using TC for more and more things, TeamCity has gotten slower and slower (And is right now crashing several times a day, without anything discernable in the logs). We have about 90 build configuration (Which isn't that much according to the documentation), and about 10 developers accessing TC on a daily basis. According to varios posts i have found on the internet this can be solved by increasing the amount of memory TC has available, that however requires switching to x64, which will then break every time we update TC.
Additionally we started using versioned configuration as a way of managing our configuration as code. This works reasonably well. However it has several glaring issues, mainly related to using different versions of configurations across branches, see https://youtrack.jetbrains.com/issue/TW-60493, on which there have been absolutely zero communication about efforts to fix things.
Furthermore the versioned scripts that are generated are not generated well enought that you can actually edit them without losing things like build history, or for moving between VCS providers.
TC is currently working so badly for us, that we are putting additional resources and effort into moving to something else, where things actually works.
There are many good things that we really love about TC, however the above are bad enough deal breakers that we have now called it quits.
Again, apologies if this is the wrong place.