Curious, if you put a game in and then remove it, do the applets still loose their banner or do things still freeze? or this only when the game cart is inserted?
If only when a cartridge is inserted then the system sounds like it hanging when trying to read the NAND / EEPROM memory on the cartridge.
If the applets normally don't always open or freeze then it sounds like eMMC corruption and that could be just wear and tear over time, maybe a update will help it, maybe it's the actually hardware eMMC starting to die, depend on how many uses but they are rated to last at least over five years or more if I recall. Though I have seen them fail earlier in a DSi and a original 3DS.
Also, I do not believe that is a slot guard at all, it in fact it appears to apply downward pressure on the card to ensure a better connection. They did however stop using that particular cartridge slot shielding and I'm sure there is a reason