Transaction Fees in Sandbox Spiking

I’m running an automated script against my Fireblocks sandbox environment to trigger a number of internal transactions as part of some testing.

The fees keep spiking out of control though as I work through the batch meaning my wallets become unable to make internal transactions because they couldn’t cover the fee.

I was seeing fees in excess of 2000 sat/vB!

Is this some way that Fireblocks uses to rate limit activity within a Sandbox account, or could this just be a wider issue.

I haven’t seen this behaviour before, however.

Thanks,

Matthew