Can you help me figure out why some files were not sent to the Heavy forwarder?

[kinaba_splunk]

The universal forwarder (UF) seems to read the following files, but the files were not sent to the heavy forwarder (HF) around 11-26-2018 16:16. The following messages appeared in UF's splunkd.log around that time. It seems that Splunk read the files.

11-26-2018 16:16:16.109 +0900 INFO TailReader - Batch input finished reading file='/fxxxx/splunk/MMM2018092615.txt 
11-26-2018 16:16:17.882 +0900 INFO TailReader - Batch input finished reading file='/fxxxx/splunk/OOO2018092615.txt

Following messages appear in UF's splunkd.log around the same time.

11-26-2018 16:16:05.005 +0900 INFO TcpOutputProc - Queue for group xxxxx_fwd_intermediate has stopped dropping events 11-26-2018 16:16:10.004 +0900 INFO TailReader - Could not send data to output queue (parsingQueue), retrying... 
11-26-2018 16:16:10.005 +0900 WARN TcpOutputProc - Queue for group xxxxx_fwd_intermediate has begun dropping events 

Could you tell me about solution?

[kinaba_splunk]

Please check if the file size is large. For example, the size is 20-180MB, it seems that the default queue size of 500KB is really low for them. So, the queue got full is an expected behavior and increasing the queue size should be a solution for that.

UF's outputs.conf 
[tcpout:xxxxx_fwd_intermediate] 
maxQueueSize = 128MB 

HF's inputs.conf 
[splunktcp://9997] 
disabled = 0 
queueSize = 128MB