Rebuild the context in two lines
State the company, role, last conversation, and any action you completed. Do not make the recruiter search an old thread to understand why you are writing.
Ask a question that can be answered
Ask whether the role is active and whether you remain under consideration. Give them permission to say the process has closed, which is more likely to produce a useful answer than a vague request to connect.
Leave the relationship intact
If there is no reply after one final check-in, thank them for the earlier conversation and move on. Avoid public accusations or contacting their colleagues about the silence.