Panel/Sprites won't update after being set inactive then reactivated - unity3d

Question

I've run through an entire fault tree trying to diagnose this, with no joy.
I'm writing a 2D card game in Unity/C#. I have four panels (one per player) that hold the cards, name, discard pile, etc. for each player. I need to have a pop-up dialog panel come up over the player panels when the user wants to change options. For some reason, I cannot get the pop-up to appear over the card sprites (it does appear over the other elements: interior panels, images, text boxes, etc.). I've tried adjust the Zpos for the dialog box panel, but nothing changes. That's problem one, but it leads to a more worrisome issue.
The bigger issue is this. Since the options panel won't display in front of the players' cards, I thought I'd just deactivate the player panels, display the dialog, then deactivate it and re-activate the player panels when it's closed. That works fine: for three of the panels. The fourth panel comes back on in its previous state, but the graphics on it will no longer update.
I've debugged and discovered the new cards are being handled correctly (sprite names changing, etc.), the discard pile is being updated, the player's name is being highlight/de-highlighted as the game progress, but none of it is appearing! It's visually stuck in the state it was when I deactivated it.
Investigating further, I've determined the error crops up anytime I deactivate and the re-activate that player's panel, whether I do it via the inspector (attaching those events to a button click), or do it in-line in script. I don't even have to open the options dialog box: I put SetActive(false/true) statements in my game code and it immediately kills the graphics updating for that panel. The sprites, text, etc. remain as they were when I deactivated and will not update.
player3Obj.gameObject.SetActive(false)
player3Obj.gameObject.SetActive(true);
Doing that to the other three panels has no effect and works fine. I see nothing different about panel 4. In fact, I can deactivate only one of its card sprites, and when I turn it back on, it is now "stuck" and won't update, even though all the other cards in that player's hand will. Same if I deactivate/re-activate one of the text fields. It will no longer update, but everything else does.
I've got no exception errors or anything, but this looks to me like some kind of memory problem, though I can't imagine what. It shows up in my Android build, no it's not specific to my machine. I'm throwing this question out there hoping someone has seen something similar.
If nothing else, maybe someone can tell me how to get my options panel to display over the card sprites. But I hate to leave a problem undiagnosed: they have a way of coming back and biting.
Update
Here's the code that isn't getting displayed. The cardBackSprit values are updating correctly, as is the gameObjectSprite, but the image onscreen isn't changing:
void DrawCardBitmap2(int Player, int cardSpot, int cardIndex)
{
string spriteObjectName;
spriteObjectName = "Sprite_Player" + Player + "_" + cardSpot;
gameObjectSprite = GameObject.Find(spriteObjectName);
gameObjectSprite.GetComponent<SpriteRenderer>().sprite = cardBackSprite;
}

Answer 1

There's a lot to unpack here. Let's break down your post into a series of questions:
1. I cannot get the pop-up to appear over the card sprites
It sounds like you're using the UI Canvas in Unity to handle your info panels for your players, but gameObjects for other elements. This is good, but the UI Canvas' sorting order is a bit different from standard game objects.
UI elements in the Canvas are drawn in the same order they appear in the Hierarchy. The first child is drawn first, the second child next, and so on. If two UI elements overlap, the later one will appear on top of the earlier one.
In order for your pop-up to appear above other elements in your canvas, they need be be higher in your scene's Canvas hierarchy.
Important to note: Canvases set to any Screen Space render mode will render over other game objects in the scene. Canvases set to World Space will render in their world position in the scene. The only render mode that uses Z Position to choose sorting order is World Space, but this is not my recommended solution to your problem.
My recommended solution:
Break your UI into multiple different canvases. Specifically, move your pop-up to a different canvas and place it higher in the scene hierarchy than your card sprites. When you enable/disable or move the pop-up, it will now appear over the card sprites.
2. Four panels (one per player) that hold the cards
From context and some of your code, it sounds like you have SpriteRenderers in your UI Canvas. This is known to be a complex rendering problem. Common advice involves using 2 cameras for rendering, and use camera depth to raise sprites over UI elements. However, redesigning your UI canvas is probably simpler.
3. Using GameObject.Find and complex strings at runtime
GameObject.Find is not performant, and it's not robust. It looks through all elements in the scene and returns the first object it finds with that name.
This poses a few problems:
You cannot have game objects with the same name anywhere in your hierarchy, even if they are nested in different places.
CPU cycles are wasted searching through all objects.
Hidden dependencies on object names that only show up during runtime.
Here's a great blog post on some better practices. I recommend using the [SerializeField] attribute and configuring it via inspector.
4. Canvas isn't updating when objects inside of it change
You can consider invoking Canvas.ForceUpdateCanvases() in LateUpdate(). This is more of a hack than an actual solution, but if this solves your problem it is likely an issue with canvas rendering. If this does not solve your problem, then this problem is likely elsewhere in your code that is currently not provided.
A canvas performs its layout and content generation calculations at the end of a frame, just before rendering, in order to ensure that it's based on all the latest changes that may have happened during that frame. This means that in the Start callback and the first Update callback, the layout and content under the canvas may not be up-to-date.