Earlier I just submitted my work to one of my clients. After that my contract are on hold for unknown reason.
Recently I just got re-activated and the client asked me to redo some of the work. My question is Should I continue to do it or not? How risks I am for not getting paid? (escrow method)
If the contract was previously on hold but is now not on hold, you can safely resume work and you're no longer at risk. Well, more precisely, you're equally at risk here as you are with the rest of your contracts.
When a client account is put on hold, all their contracts are also put on hold, regardless of whether they are hourly or fixed rate.
The fact that the contract was quickly resumed means that whatever the issue may have been has been resolved, so I would not worry about it.
It happens from time to tie, more often with some clients than others, and in my personal experience it is usually quickly resolved.