+x+xSorry, there are quite a lot of images included in this task, so it’s difficult to upload them all. Would the task link work instead?
Here is the link to the task:
https://mili2nd.eu/utlc
> there are quite a lot of images included in this task, so it’s difficult to upload them all
In this case, the link works, but generally: zip them up, attach the zip archive.
Not seeing an obvious issue with the code per se and it's working fine on my test system, though I do wonder why you're doing this indirection, which seems unnecessarily complicated and fickle:
<picture category_gift>
/ items = ("<%values.category_gift_stim%>")
/ size = (4.5cm, 4.5cm)
/ position = (50%, 50%)
</picture>
with
<list Category_Gift>
/ items = ("mask04.png", "dreamcatcher.png", "christmastree.png",
"masquerademask01.png", "toynutcracker.png", "horsefigurine.png",
"ribbon04.png", "ribbon03a.png", "snowglobe.png",
"vase03.png", "candle08b.png", "bust.png",
"trophy01.png", "cross01.png", "trojanhorse.png",
"pouch01b.png", "piggybank.png", "amphora.png")
/ selectionMode = values.itemNumber
</list>
Why not go the direct route, namely
<picture category_gift>
/ items = ("mask04.png", "dreamcatcher.png", "christmastree.png",
"masquerademask01.png", "toynutcracker.png", "horsefigurine.png",
"ribbon04.png", "ribbon03a.png", "snowglobe.png",
"vase03.png", "candle08b.png", "bust.png",
"trophy01.png", "cross01.png", "trojanhorse.png",
"pouch01b.png", "piggybank.png", "amphora.png")
/ select = values.itemNumber
/ size = (4.5cm, 4.5cm)
/ position = (50%, 50%)
</picture>
which would save you numerous values, lists, and the whole <picture preload > setup.
Regardless, that isn't the issue. What likely is the isssue is that your system is running low on memory and dropping frames as a consequence. I've seen this on a few extreme cases on some Macs and iPads, usually a couple generations old.
Your images are excessively large -- they have 2000 x 2000 pixel resolution, which you do not need, because you have them only cover a tiny section of the screen. They clock in at between 0.5 and over 5MB *per image* at that resolution, and they'll eat a lot of memory unnecessarly. Convert them to a sensible resolution, something like 500 x 500 pixels. That'll save memory, incur no quality loss, and will improve startup time as well, because your participants don't have to download 100s of excess MBs, which then have to be pushed into memory.
Try that. And if after you're still seeing a problem, make a note in your test runs of precisely which images are omitted and post the result here.