My first thought was 'over watering.' Poke a couple holes in the bags for drainage.

my first thought was not enough water but could be leaf scorch. in the morning are there droplets of water on the leaf edges? if yes then it is probably sun scorch. if they are standing in water they need better drainage as Bathgate says.

Thank you. plants not looking good.

I suggest starting new plants. Depending how advanced the problem is, cucumbers may not recover or ever produce quality fruit you'd want eat. Start new plants while it's early. Be sure to use clean, sanitized materials.