onError occasionally not called - rx-java2

Question

I have an issue with one of my onError handlers occasionally not being called, leaving my application in a kind of lingering state.
This is my code
tokenSubscription = Observable.interval(pluginProperties.getRefreshTokenInterval(), TimeUnit.MILLISECONDS, Schedulers.io())
.subscribe(x -> {
ConversationContextV3 contextV3 = (ConversationContextV3) authenticationContext.getConversationContext();
refreshAccessToken(contextV3);
},
error -> {
logger.error("Exception after retrying refreshing session token, will attempt to reconnect");
disconnect();
}
);
When refreshAccessToken() is called it sometimes throws an exception, which is then handled in onError. Below is the expected output. Notice the last to lines.
2017-09-04 20:11:27.750 [RxCachedThreadScheduler-82] DEBUG c.danlind.igz.brokerapi.BrokerLogin - Refreshing access token
2017-09-04 20:11:27.798 [RxCachedThreadScheduler-82] ERROR c.danlind.igz.adapter.RestApiAdapter - Exception when refreshing session token
org.springframework.web.client.HttpServerErrorException: 503 Service Unavailable
at org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:94)
at org.springframework.web.client.RestTemplate.handleResponse(RestTemplate.java:700)
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:653)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:613)
at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:531)
at com.danlind.igz.ig.api.client.RestAPI.refreshSessionV1(RestAPI.java:778)
at com.danlind.igz.adapter.RestApiAdapter.refreshSessionV1(RestApiAdapter.java:281)
at com.danlind.igz.brokerapi.BrokerLogin.refreshAccessToken(BrokerLogin.java:80)
at com.danlind.igz.brokerapi.BrokerLogin.lambda$startRefreshAccessTokenScheduler$17(BrokerLogin.java:99)
... (removed some lines for brevity)
2017-09-04 20:11:27.811 [RxCachedThreadScheduler-82] ERROR c.danlind.igz.brokerapi.BrokerLogin - Exception after retrying refreshing session token, disconnecting
2017-09-04 20:11:27.811 [RxCachedThreadScheduler-82] INFO c.danlind.igz.brokerapi.BrokerLogin - Disconnecting from IG
My issue is that sometimes it seems like onError is never called, leaving me with a log output like this:
2017-09-04 20:11:27.750 [RxCachedThreadScheduler-82] DEBUG c.danlind.igz.brokerapi.BrokerLogin - Refreshing access token
2017-09-04 20:11:27.798 [RxCachedThreadScheduler-82] ERROR c.danlind.igz.adapter.RestApiAdapter - Exception when refreshing session token
org.springframework.web.client.HttpServerErrorException: 503 Service Unavailable
at org.springframework.web.client.DefaultResponseErrorHandler.handleError(DefaultResponseErrorHandler.java:94)
at org.springframework.web.client.RestTemplate.handleResponse(RestTemplate.java:700)
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:653)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:613)
at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:531)
at com.danlind.igz.ig.api.client.RestAPI.refreshSessionV1(RestAPI.java:778)
at com.danlind.igz.adapter.RestApiAdapter.refreshSessionV1(RestApiAdapter.java:281)
at com.danlind.igz.brokerapi.BrokerLogin.refreshAccessToken(BrokerLogin.java:80)
at com.danlind.igz.brokerapi.BrokerLogin.lambda$startRefreshAccessTokenScheduler$17(BrokerLogin.java:99)
... (removed some lines for brevity)
My code feels pretty straight forward, I can't really understand what would cause this "glitch"? Any ideas? Using RxJava 2.10