Rengar bug

I was playing Rengar and each time I would ult, my screen wouldn't go dark showing i'm stealthed. One time i ulted to gank bot lane, support exhausted me even though i wasn't near a control ward nor tower so i don't know how she saw me to exhaust me. Then each time i ulted, i was scared to move near an enemy because my screen wasnt dark so i wasnt sure if i was in stealth or not. I asked my team if they saw me in stealth when i ulted and they were like "i guess" so not entirely sure what happened that match

Does anyone know anything about this? I may have not explained correctly so sorry if this doesn't make sense to you