You may be overreacting a little bit. The posture I see in the bath is normal and the leg stretching out is your frog attempting to lunge forward and not quite getting anywhere. I did not see any actual twitching or spasms that would be related to illness or disease.

You could provide a little extra calcium for a couple weeks just to see if anything changes, but as of now I do not believe you need to worry unless the frog loses control of the leg muscles and the leg begins to move and spasm constantly.

I would like to see a video of the frog moving around in it's enclosure. Especially like you described when the frog was getting back into it's burrow.

Keep us posted.