Harman Mark III Grate Question

Been using a Harman Mark III since winter of 2014/2015. This year was the first year twice I had my grate get stuck where the only solution was to let the fire burn out, clean everything out remove the fire bricks and eventually I was able to work them loose. Today I had to do it the second time and had to use liquid wrench penetrating oil to get the back most grate out. Is this simply an issue that the area where the grates are cradled needs cleaned yearly (first time I had them out since 2014) or is something else amiss? I never had this issue until this year. I do think the coal I got this year was smaller than Nut coal previous years...could that be the culprit? Is there anything I can do to the grate ends before putting them back into the cradle...? Any advice is appreciated. Thanks!

Got a pic of how those grates sit/fit in?

Something's definitely wrong, I have had a Mark One since 2006 and have never had the grates jam to the point where I've had to take it apart, have burned all sizes of coal in it, even some rice when I ran out of nut (it doesn't work very well).
I've had stones jam the grates, but I can usually free them up with a wire poker from underneath and some patience.

It's possible to get a smaller stone that look black going in then jams the grates leaving a full drop in the pan and good luck finding that piece. So far I haven't had that happen to the Harmon SF250.