Thank you! With this information, I realized my problem is actually not directly related to deadlocks, but no exception is being raised (even due to syntax error, etc). I eventually came to the realization that the ordering of try/using seems to be important for catching the exception.

IE this exception is not caught:

private async Task<bool> UpdateSessionInDatabase(...)
{
	try
	{
		using (var command = new MySqlCommand(updateString, Database.db))
		{
			// ...
			int result = await command.ExecuteNonQueryAsync();
			// ...
		} 
	} catch (Exception ex)
	{
		// This does NOT trigger
		Debug.WriteLine("Exception: " + ex.Message);
	}
}

However, by swapping the ordering of try vs using, this exception is caught:

private async Task<bool> UpdateSessionInDatabase(...)
{
	using (var command = new MySqlCommand(updateString, Database.db))
	{
		try
		{
			// ...
			int result = await command.ExecuteNonQueryAsync();
			// ...
		}
		catch (Exception ex)
		{
			// This DOES trigger
			Debug.WriteLine("Exception: " + ex.Message);
		}
	} 
}

Do you know, is this expected or something weird with my code?

I think something is weird with your code. I can't reproduce this problem:

class Program
{
	static async Task Main(string[] args)
	{
		using var connection = new MySqlConnection("Server=localhost;Uid=root;Pwd=pass;");
		await connection.OpenAsync();

		var program = new Program();
		var result = await program.UpdateSessionInDatabase(connection);
		Console.WriteLine("Result: " + result);
	}

	private async Task<bool> UpdateSessionInDatabase(MySqlConnection db)
	{
		try
		{
			using (var command = new MySqlCommand("bad sql", db))
			{
				int result = await command.ExecuteNonQueryAsync();
				return true;
			} 
		} catch (Exception ex)
		{
			// This does NOT trigger
			Console.WriteLine("Exception: " + ex.Message);
			return false;
		}
	}
}

prints:

Exception: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'bad sql' at line 1
Result: False

If you can produce a small repro that shows that MySqlConnector doesn't throw exceptions, please open a new issue with that code.

Thank you; yep, it was my code indeed

Just FYI if you are curious, it was a combination of three issues:

1. Async methods that aren't awaited don't get exceptions handled in the expected place due to how .net translates exception handling in async functions -- ie, this:

If you do not wait on a task that propagates an exception, or access its Exception property, the exception is escalated according to the .NET exception policy when the task is garbage-collected.

2. vscode debugger not consistently printing exception debug output when they happen at end of execution of an async program (I think related to C#'s exception state machine translation happening above)
3. Simple mistake of accidentally using Debug.WriteLine instead of Console.WriteLine and so thinking exceptions weren't getting called in production

My program now seems to be working well after:

1. Implementing retry logic and try/catches (to handle deadlock)
2. Changing main method to be async and use await (so exceptions are caught)
3. Double checking I had no async voids, as those also wouldn't handle exceptions
4. Fixing debug.writeline -> console.writeline so exception output would be shown in production

Thanks again for your help and tips while I learned up about all of this :)