This will be futher clarfied in the new rules:
If you are unable to maintain the pace of the Safety Car during an Safety Car Period, you are not entitled to keep your position.
Case examples:
Car in P4 of 12 spins, recovers and rejoins in P9. The driver may not return to P4, but must hold in P9.
Car in P1 of 20 pits, and exits the pits in last. That car will be restarting in last.
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