Thanks for the quick help. I managed to resolve the issue myself:
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First, I changed the IPv6 address from "Public IP" to "Static IP Address".
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Then, I used the "Reconfigure Networking" function in the Solus VM panel provided by the VPS provider.
I have since switched the IPv6 setting back to "Public IP" and the issue has not recurred. I assume that the "Reconfigure Networking" function resolved the problem.