This memory card hasn't have autoconfiguration of memory. You need to set jumpers to configure the memory.
I shall explain what the card does when you put a 1 MB memory and jumpered with 4 MB.
The Amiga shows the 4 MB, but when you use more RAM, it will crash.
Do you have a SCSI controller on your GVP 1208?
My GVP 1208 has been expanded with 2x 4MB, SCSI controller and 28 MHz FPU.
Great card, but doesn't have a realtime clock unit and like other memory cards, it isn't PCMCIA friendly.