Unable to pedal when in high gears
The chain is stuck because of its short length and cross-chaining - the chain links are severely bent. Also with the chain not clean it will not turn nicely in such a scenario:



Also your chain is short, making your derailleur stretch forward (marked blue) which makes the cross-chaining even more severe (marked red). On such a stretched derailleur there are bad side forces (maybe the little wheels in the derailleur get stuck while being bent).

For old drive trains cross-chaining was not accounted for as it is bad practice. Such rear derailleurs usually doesn't have a range like new ones. New bikes are designed to handle cross-chaining and such a chain would be definitely too small for them, but for old bikes it's more complicated. Looking at first picture where you have small-ring + small-gear (the shortest chain length) your derailleur could accommodate for a bit longer chain making the setup safer if you accidentally shift into big-ring + big-gear.

You can have the same gear ratio using other gears instead of cross-chaining:



You can see that 48T front 32T back (big-big) gives the same ratio as 36T front 24T back (middle-middle) which makes the chain straight.

The not-cross-chaining rule:


for small chain-ring use only the bigger half of your cassette
for middle ring you can use all your cassette
for big ring use only the smaller half of your cassette


In practice it's even less as this table of gear ratios explains (this is for 44-32-22 crank and 11-32 teeth cassette):



You only need to cover with the big and small ring what cannot be covered with the middle ring. See how this XTR9000 Di2 Syncro-Shift is shifting. When it shifts the front it also shifts the back at the same time, and it prevents cross-chaining. This video also shows gearing efficiency.