Those prototyping boards are susceptible to bent contacts. If a thick wire is used it can open the contacts, then when a thinner wire is used, that contact may be intermittent. Worn contacts may also be a problem as oxide forms on the base metal.
When a circuit does not work, test the contacts by inserting a long link in parallel with the suspect link, use different holes in the same bars.
Look under the board. It is usually possible to remove the base to access the connector bars, remove a bar, clean out the dirt, then carefully bend the spring contacts back into shape.
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