Password masking only works for JDBC Connectors

We have set our Kafka Connect to be able to read credentials from a file, instead of giving them directly in connector config. This is how a login part of connector config looks like:

"connection.user": "${file:/kafka/pass.properties:username}",

"connection.password": "${file:/kafka/pass.properties:password}",

We also added these 2 lines to "connect-distributed.properties" file:

config.providers=file

config.providers.file.class=org.apache.kafka.common.config.provider.FileConfigProvider

Mind that it works perfectly for JDBC connectors, so there is no problem with the pass.properties file. But for other connectors, such as couchbase, rabbitmq, s3 etc. it causes problems. All these connectors work fine when we give credentials directly but when we try to make Connect to read them from a file it gives some errors. What could be the reason? I don't see any JDBC specific configuration here.

EDIT:

An error about couchbase in connect.log:

[2021-12-02 11:50:19,580] ERROR [com.couchbase.io][SaslAuthenticationFailedEvent][20ms] Authentication Failure - Potential causes: invalid credentials or if LDAP is enabled ensure PLAIN SASL mechanism is exclusively used on the PasswordAuthenticator (insecure) or TLS is used (recommended) {"circuitBreaker":"DISABLED","coreId":"0xbf785c7500000001","remote":"10.30.142.109:11210","status":"UNKNOWN","type":"KV","xerror":{"ref":"ae3ce600-7097-4077-9231-8ced290cd399"}} (com.couchbase.io:533)
[2021-12-02 11:50:19,580] WARN [com.couchbase.endpoint][EndpointConnectionFailedEvent][23ms] Connect attempt 9 failed because of AuthenticationFailureException: Authentication Failure - Potential causes: invalid credentials or if LDAP is enabled ensure PLAIN SASL mechanism is exclusively used on the PasswordAuthenticator (insecure) or TLS is used (recommended) {"circuitBreaker":"DISABLED","coreId":"0xbf785c7500000001","remote":"10.30.142.109:11210","type":"KV"} (com.couchbase.endpoint:523)
com.couchbase.client.core.error.AuthenticationFailureException: Authentication Failure - Potential causes: invalid credentials or if LDAP is enabled ensure PLAIN SASL mechanism is exclusively used on the PasswordAuthenticator (insecure) or TLS is used (recommended) {"circuitBreaker":"DISABLED","coreId":"0xbf785c7500000001","remote":"10.30.142.109:11210","status":"UNKNOWN","type":"KV","xerror":{"ref":"ae3ce600-7097-4077-9231-8ced290cd399"}}
        at com.couchbase.client.core.io.netty.kv.SaslAuthenticationHandler.failConnect(SaslAuthenticationHandler.java:488)
        at com.couchbase.client.core.io.netty.kv.SaslAuthenticationHandler.maybeFailConnect(SaslAuthenticationHandler.java:293)
        at com.couchbase.client.core.io.netty.kv.SaslAuthenticationHandler.channelRead(SaslAuthenticationHandler.java:250)
        at com.couchbase.client.core.io.netty.kv.MemcacheProtocolVerificationHandler.channelRead(MemcacheProtocolVerificationHandler.java:84)
        at java.lang.Thread.run(Thread.java:748)

It says something about authentication but works fine when credentials are given directly. If the masking is not working correctly, how does it work for JDBC connectors?