Hi @EmbeddedTech
Thank you for reaching out again!
As I have been checking, our SDK does not contain the source code of the APPW_CreatePersistentScreens() function, so I can not inspect how it handles memory, the AppWizard User Guide & Reference Manual does not details this.

I would recommend isolating the issue, trying the FlexSPI demos in your application and measuring how much time do you need to take to load a buffer from Flash, or copy and write buffers.
Additionally, consider if you have any cache enabled, and try the results by disabling it. Check that you are using QSPI, and not standard SPI mode. Check if the Emwin libraries are not getting out of available SRAM or something related.
Anyway, I would recommend inquiring also with Segger about this, as they may be able to provide more details about the operation of the function.
I am sorry that I do not have more further insights at this time.
Diego