On one of my 3 computers that are running eMClient, the Trash folder is missing many emails. I don’t have any rules configured for the Trash folder. The other 2 computers Trash folder are in sync. Windows 10 Pro, Client Version 7.2.36908.0
Trash is not something that most people want to sync. 
But there may be some message corruption in the eM Client database. Right-click on the Trash folder and choose Properties > Repair.
I completely disagree. The folder is supposed to sync. It’s a paid product and I expect it to function as advertised.
If for some reason, as I said above, it has not synced, please try my option above.
Otherwise, if you don’t want answers to your questions, don’t ask them on this forum. As a Pro License user take advantage of your VIP support option and open a ticket directly with eM Client.
I don’t recall stating that I didn’t want answers to my questions. Your original “suggestion”, (most people don’t care about trash folder syncing), wasn’t really helpful. Ticket has been open for over 48 hours with no response from EmClient.
Sorry about my comment; it was not meant to be a solution to your problem, but a light-hearted comment. The emoticon that follows indicates this, but is is true never-the-less and actually quite amusing if you think about it. (The emoticon indicates that I am winking, which indicates that I am both amused and sympathetic to the whole situation. Just in case anyone was wondering what those odd characters mean. Not like LOL which means laughing out loud, but is somewhat unclear as to the intent, and I always thought could be considered mocking, which I am not in this thread. I don’t think there is actually a specific emoticon for amused, though there certainly are emojis)
But on a more serious note, what is the date and time you opened your ticket? You can find it in the ticket header as in the screenshot below. eM Client Support should answer within 24 hours of that but now it is the weekend, so they are not working. e.g. If you open a ticket at 5pm on Friday, it is unlikely you will get a reply before late Monday or even first thing Tuesday. Not that you did open it on Friday, but most likely on early on Thursday, right? If you don’t get an reply on Monday, login to the support page and change the priority of the ticket to medium. See the priority option in the screenshot below. Also, if you did not open the support ticket under the address you used to purchase the Pro License, you may not get a response at all.
But you never did say if the repair option worked? If the message database is corrupt, or there is some other error, there are a few other options to get everything working again. I’ll leave it to Support to assist you further.