Lash extensions & hot tub

I had a new client last week for Russian Volume lashes. I gave her the full aftercare advice including avoiding any heat treatments for 48 hours.
The client had the lashes applied on the Tuesday. On the Friday she went in the hot tub. Saturday the lashes started to fall out, and continued to fall out over the next few days.
I have been doing lashes since November last year and never had any problems like this before.
Then again I’ve never had a client use a hot tub whilst wearing lash extensions before.
Has anyone else experienced this or have any advice for me please?