Why did Ward miss out on a couple of championship seasons?
Not sure exactly what you mean.
Are you asking why he wasn't in the first tranche of SG2 officials ?
If so the answer is he wasn't good enough. He barely is now.
(I know that didn't stop them appointing a load of other SG2s who weren't good enough either.)
I was meaning why, after doing quite a few seasons in the championship, did he not referee any championship games after the 2015/16 season until this season. Was he demoted, injured......?
Simply because the Select Group 2 was formed from the start of season 16/17, with only a small number of officials added to it. Since 16/17 championship games are only refereed by either SG1 (the PL refs) or SG2 (the Championship refs). He was not selected for SG2 initially so therefore did not do Championship games.