loosely speaking, this means your disk is unable to process the amount of data handed over by the CPU in an appropriate amount of time. Especially on cheap SD cards, this is a common issue.
You might get better performance by using a different SD card (some of them are “optimised” for cameras saving raw images, which should be good enough, although they are more expensive). In the end, however, choosing a different hardware which is capable of booting from an SSD might be the more sustainable solution.
I use a Samsung 16GB HC class 10. Does it qualify as cheap ?
In any case I assume the internal eMMC should have better performance hence…
re: boot ipfire on eMMC, the instructions in the ipfire wiki do not work for me, however the above comment recommends the boot switch must happen against the SDCard rather against the eMMC… which means the correct boot switch instruction should be