One of your issues, next to the step, looks like settlement. It could be caused by an installation defect. Or it could be caused by water washing out the base. We can't see everything about this area. A person would need to explore it in order to determine the cause and solution. Your retaining edge doesn't look attractive or sufficient. Base could be "leaking" out of either end during rains, as water washes along the board, below the pavers and then out the ends. Given the fact that pavers are sinking above and below the riser edge, points further to water washing out the base as being the culprit.

I would rebuild the step, eliminating the board edge entirely. Instead, the straight edge of the pavers would be the edge. A concrete curb-type affair could be what supports them. (Or some type of masonry structure if you prefer that.)

In the first picture, where pavers look like they're being pushed up by a tree root (toward the table) you can dig down just outside the edge of the patio and inspect to see if, in fact, there is a tree root there. If there is, cut it a few inches outside of the patio with a folding pruning saw (they are the easiest to use when cutting roots.) It takes a lot longer for the process of decay to attack the root than it does for the root to grow in the first place. If you can tolerate the pavers as they are, they would improve over time as the root decomposes and shrinks. It could happen slowly over a year or two. You might notice some difference in 6 months. If you can't tolerate the slow shrinking process, there's no other way to fix it than tearing up that section of patio, rebuilding the base and resetting the pavers.

Considering that when stop sign pavers were popular Tupac was still alive, I'd say you (or whomever installed them) got a lot of value from them. There were a lot of practices we did in those early, dark days of pavers that we don't do now because they cause the problems you have - wood bender board as edging, no border on a small footprint paver, etc. And a 2x as a step edge is bonkers even for back then. Here are my thoughts:

• agree w/ Yard on the tree root issue. Pulling up the pavers and removing the whole root is ideal, but it takes skill to re-lay pavers to tie into an existing surrounding patio. Just that is probably a full day for a skilled crew, especially because on an old patio it's like pulling a thread on a sweater - you have to cut it off somewhere or you unravel the whole thing
• on the step, I'd suggest something like a Techo-Bloc Rocka step (however many are needed for the length of the edge). It's easy to place and level, will do a great job of retaining the landing above, and when you have the budget to replace the patio they can be reused. Because they only weigh around 350 lbs, they can be wheeled into existing landscapes with machinery.
• I'd still consider budgeting for replacing the patio on the sooner side. It's in rough shape, it could be prettier, and it could be more functional. Based on the agapanthus in the foreground I'm assuming you're someplace where the weather is good for being outdoors most of the year, so this could be a wonderful extension to your home.

As far as a more suitable material, it all comes down to installation. If this was a concrete or stamped concrete patio, that tree would've cracked and heaved the slab and repair wouldn't even be on the table as an option. A local landscape designer can recommend the best materials and layouts to fit your style and your budget.

@Tiffany Chi. You've received solid diagnosis and assistance from two experts in Yardvaark and Revolutionary Gardens.

I add photos only to provide a visual for you regarding step options. The installation below is with monolithic cast steps meant to look like natural limestone. They are Unilock Ledgestone.

The next photo is a built or constructed step, but also from Unilock Ledgestone. The treads are jointed, not solid like the first photo. Not the greatest photo but it shows the distinction between the first two.

Glen Ellyn Landscape · More Info

Lastly, this is a masonry step with concrete footing and rock-faced limestone coping. This is the most expensive option but one that should last for a lifetime or two.

Transitional Patio · More Info

A good local contractor/designer will be able to help you navigate through the process. Good luck.

Excellent photo advice K&D!