Requesting random number on Chainlink Testnet and getting zeroes

I have been working on something that encapsulates chainlink random number on nfts to provide them to users, using a chainlink subscription and adding my smart contract as a comsumer. When working on testnet I am finding some times it gives me zero numbers and not a random one. This behaviour is random. Subscription is funded and smart contract added as a comsumer.

May this happen on mainnet also?

is there any warranty the request random number operation finishes succesfully, or how can I take care of it on my code?

Thanks in advance!

Subscription is funded and smart contract added as a comsumer. geting some times zero numbers and not a random one