T8 user, starting to get blade dishing by heel

[av8r]

I've been using my T8 with the supplied stone wheel for a few years.  This weekend I sharpened about 40 knives for family/friends and some ended up with some "dishing" (may not be the correct word) near the heel of the blade.  I check the true of my wheel before every session and don't apply heavy pressure (I think) when sharpening.  2 of the knives are my own kitchen knives and I've not noticed this happening before.  Any suggestions on what to look for or change in my technique?

[Sir Amwell]

By dishing do you mean à slight recurve or as I call it a smile?
Is this happening on all knives or particularly those with bolsters?
If it's a general occurrence I would suggest alternating your passes each time, don't work one side of the blade until you get a burr and then go to the other side. Work each side of the blade one pass, heel to tip then flip. Heel to tip on the other side then flip, one pass etc.
If it's bolstered knives in particular then you are over grinding at the heel due to the bolster getting in your way. Consider grinding down that bolster unit it is no longer impacting the process.
I don't think it's your stone causing this unless it's very much out of true. At the very least re square it to eliminate this variable.
I had a similar problem to start with but the practice of continually flipping the blade after each pass largely put paid to this problem. You will find a way with your technique to stop this happening.