Glad to hear you found a fix. It’s still definitely a macOS bug if it isn’t re-establishing the PPPoE connection after waking from sleep, but since you have found a workaround, it’s now somebody else’s problem 
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In general, however, I would recommend that everybody using broadband have a router between their computer and their service provider network. There are many reasons for this, including:
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Network Address Translation. Which allows you to connect multiple devices to your feed, all sharing a single IPv4 address - so you don’t need to pay for multiple addresses.
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As a side effect of NAT, you also get some security. Unsolicited inbound packets (that is, those not part of an active session) get discarded because the router can’t figure out what to do with them.
Although IPv6 is generally not translated, IPv6 is not really insecure. This is because most ISPs issue a 64-bit block of addresses to each customer, and your computers pick random addresses from within the block. So simple port-scanning attacks (used on IPv4 address blocks to look for vulnerabilities) are impractical, since you’re only using a small number of addresses from a pool of 18 pentillion (that is 18 million trillion) addresses, a port-scan capable of a million addresses per second would still take over 500,000 years to find your computer.
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Most routers have some degree of firewall capability, although that will vary from model to model.