I use Jolla with /home/nemo mounted from 16gb sdcard, formatted as ext4, and it works perfectly.

Then I've bought 64gb sdcard (sony), created a Linux partition with cdfisk, formatted as ext4, and rsynced information from the old card to the new one.

Since that, some software, let's say Sailfish browser hungs from time to time.

It is possible to minimize it, the software, I guess, does i/o, and hungs at that time.

I've checked the speed of sdcard with hdparm and it's perfectly okay.

I've formatted it again, this time made a tar archive from the old one, and unpacked the tar archive to the new one. Again, sometimes it hungs.

I've tried to run vmstat, and see what's going on and may be there is a correlation between context switches that raise to 1500-2000 and that's when the application becomes unresponsive.

Of course Sailfish dialog appears, it asks what to do - wait or kill the application. Wait always helps, it just comes back soon. Sometimes in 15 seconds.

And this never happened with the 16GB card?

There's no technical reason whatsoever that would cause it. I have heard that on some cards the factory format is such (usually exfat) that it should not be wiped&reformatted to other filesystems or performance will suffer somewhat but it should not cause anything that extreme.

what are the make/model of your cards, and have you tried any other?

added mount options noatime,data=writeback,barrier=0,nobh - it looks like it helped to some extent, somtimes hungs don't happen, and when they happen it seems that they last shorter. but still.

may it be, that i've made mkfs.ext4 on a laptop with newer kernel and mkfs versions, and the old driver has problems with ext4 formatted with newer tools?

Should not really be a problem since ext4 is ext4, regardless of the filesystem tools version. All should be compatible.

Of course to be sure, you could reformat the card on the device and see if it makes any difference.

I would suggest comparing random 4kB read/write on both cards.