SPI flash trouble

Hey all, I've put Espruino on a smartwatch (SN80-Y from Yfit) and have figured out most of the pins and components (lcd, accel, touch) but am having trouble getting the XTX XT25F32B (4MB flash) chip to be reliable. Verified the following pins using multimeter: CS=D19, SO=D18, SI=D17, CLK=D20. Doing a wakeup, followed by getting vendor ID and capacity seems fine:

>  spif = new SPI();
=SPI: {  }
>  spif.setup({sck: CLK, miso: SO, mosi: SI, mode:0, baud: 8000000});
=undefined
>  spif.send([0xab], CS);
=new Uint8Array([255])
>  print(spif.send([0x90,0,0,1,0,0], CS));
new Uint8Array([255, 255, 255, 255, 21, 11])
=undefined
>  print(spif.send([0x9f,0,0,0], CS));
new Uint8Array([254, 11, 64, 22])
=undefined

That seems fine:22 at the end should mean 2^22 bits, or 4MB. So i've included it in my board file. In the devices section I have:

  'SPIFLASH' : {
            'pin_sck' : 'D20',
            'pin_mosi' : 'D17',
            'pin_miso' : 'D18',
            'pin_cs' : 'D19',
            'size' : 4096*1024, # 4MB
            'memmap_base' : 0x60000000 # map into the address space (in software)
  }

And when flashed I see:

>require("Storage").getFree()
=4194304

I then use this test script just to read the first few blocks of 256 bytes:

CS=D19, SO=D18; SI=D17; CLK=D20;

setTimeout(()=>{
  spif = new SPI();
  spif.setup({sck: CLK, miso: SO, mosi: SI, mode:0, baud: 8000000});
  spif.send([0xab], CS);
  print(spif.send([0x90,0,0,1,0,0], CS));
  print(spif.send([0x9f,0,0,0], CS));
  let hex = (d) => { return ('0'+d.toString(16)).slice(-2);};
  let buf = new Uint8Array(256);

  // 3 byte address: 0x7f 0xff 0xff (0x7f = 8MB, 0x3f = 4MB, 0x1f = 2MB)
  for(let b1=0; b1 < 1; b1++) {
    for(let b2=0; b2 < 5; b2++) {
      let bufstr = '';
      for(let b3 = 0; b3 < 256; b3++) {
        res = spif.send([0x03, b1, b2, b3, 0], CS);
        buf[b3] = res[4];
        bufstr += ("0"+buf[b3].toString(16)).slice(-2)+" ";
      }
      print(`${hex(b1)} ${hex(b2)} ${hex(b3)}: ${bufstr}`); //${btoa(buf)}`);

    }
  }
}, 1000);

The timeout was added because I was running into issues without it. This seems to work if I save it to RAM, as I get data (remnants from previous attempts to write):

new Uint8Array([255, 255, 255, 255, 21, 11])
new Uint8Array([254, 11, 64, 22])
00 00 00: 04 04 00 00 54 45 53 54 ...
00 01 00: 64 65 65 70 20 73 6c 65 ...
00 02 00: 4c 4b 7d 20 20 41 42 3d ...
00 03 00: 70 69 66 2e 73 65 6e 64 ...

In the first line you can see the ASCII for "TEST" which was the name of the file I attempted to write in the IDE.
So the problem is when I try to save the test code to Storage (or Flash):

|  __|___ ___ ___ _ _|_|___ ___
|  __|_ -| . |  _| | | |   | . |
|____|___|  _|_| |___|_|_|_|___|
         |_| espruino.com
 2v12.925 (c) 2021 G.Williams
Espruino is Open Source. Our work is supported
only by sales of official boards and donations:
http://espruino.com/Donate
>
FW addr 0x00000000 fail
Status 0
Uncaught Error: File already written with different data
 at line 1 col 1106
...{\n    for(let b2=0",0,1349);
                              ^
Uncaught Error: Too much data for file size
 at line 2 col 380
...    }\n  }\n}, 1000);",1024);
                              ^
 ____                 _
|  __|___ ___ ___ _ _|_|___ ___
|  __|_ -| . |  _| | | |   | . |
|____|___|  _|_| |___|_|_|_|___|
         |_| espruino.com
 2v12.925 (c) 2021 G.Williams
Espruino is Open Source. Our work is supported
only by sales of official boards and donations:
http://espruino.com/Donate
new Uint8Array([112, 105, 102, 46, 115, 101])
new Uint8Array([32, 104, 101, 120])
Uncaught SyntaxError: Unexpected end of Input
 at line 42 col 18 in TEST
    for(let b3 =
                 ^
> 

The other notable thing is that the CLK and SI lines are shared with the LCD (also SPI) and the accelerometer (I2C). However, I have not initialized either of those. In other tests, LCD works fine as does the accel, but I'm trying to leave out any issues with line sharing.

Any pointers greatly appreciated!