Gotchas

Use this page only for library-specific caveats.

Use the shared KV Host Link Troubleshooting & Codes page for common connection, profile, address-shape, write-permission, and PLC error-code symptoms.

Current library-specific caveats

Area	Symptom	Guidance
IPv6 endpoint	Construction rejects an IPv6 literal, or a hostname has no usable address.	Host Link connections are IPv4-only. Use an IPv4 literal or a hostname with an IPv4 result.
Bracketed IPv4 endpoint	Construction rejects an address such as [192.168.250.100].	Remove the brackets and use 192.168.250.100.
Ambiguous write result	HostLinkOutcomeUnknownError is thrown after transmission may have begun.	Do not retry automatically. Inspect Reason, determine PLC state safely, and explicitly reopen only when appropriate.
UDP duplicate response	A delayed or duplicate datagram arrives after the pre-send queue check.	Host Link UDP has no transaction ID, so the narrow check-to-send race cannot guarantee response association. Use TCP when strict association is required. UDP anomalies discard the socket but retain the resolved logical endpoint for the next request.
Named aggregate timing	ReadNamedAsync or one PollAsync cycle uses multiple wire reads.	Results are non-atomic. Use a single-request read or a PLC-side snapshot/handshake when values must share one coherence point.
Bit-in-word write	WriteBitInWordAsync or WriteBitInExpansionUnitBufferAsync can overwrite a concurrent change to another bit in the same word.	These explicit helpers are two-request, non-PLC-atomic read-modify-writes. Use PLC-side coordination or exclusive whole-word ownership, and never automatically retry an outcome-unknown result.
Device-comment encoding	Host Link RDC payloads do not identify their text encoding.	Use HostLinkCommentEncoding.Utf8 or .Cp932 explicitly, or use ReadCommentBytesAsync when the encoding is not known. Malformed selected text is rejected without fallback or replacement.