I don't know if this is related to the problem I am facing. But from time to time the size backed up hangs. I restart Arq Agent and things come back to normal for about 10 minutes. Then, the cycle repeats.
I have changed the logs to Trace and have found the following behaviour being logged:
Mar 18 12:37:13 Alisson-Pelucios-MacBook-Pro Arq[96568]: TRACE [thread 1603] 0x1000df520 Process.m:126 Process with CFBundleIdentifier = com.haystacksoftware.ArqAgent is running
Mar 18 12:37:14 Alisson-Pelucios-MacBook-Pro Arq[96568]: TRACE [thread 8c77] 0x102a7b530 BufferedInputStream.m:79 <BufferedInputStream <FDInputStream fd=14 /Users/sellaro/Library/Arq/Cache.noindex/1288h2gepgcjx1gcg482-com-haystacksoftware-arq-sa-east-1/7EA780CA-6643-4ACC-9A4B-798781656161/inprogress/todo.txt> EOF after 0 of 1 bytes received
Mar 18 12:37:14 Alisson-Pelucios-MacBook-Pro Arq[96568]: TRACE [thread 1603] 0x1000df520 Process.m:126 Process with CFBundleIdentifier = com.haystacksoftware.ArqAgent is running
Mar 18 12:37:15 Alisson-Pelucios-MacBook-Pro Arq[96568]: TRACE [thread 8c77] 0x102a7b530 BufferedInputStream.m:79 <BufferedInputStream <FDInputStream fd=14 /Users/sellaro/Library/Arq/Cache.noindex/1288h2gepgcjx1gcg482-com-haystacksoftware-arq-sa-east-1/7EA780CA-6643-4ACC-9A4B-798781656161/inprogress/todo.txt> EOF after 0 of 1 bytes received
Mar 18 12:37:15 Alisson-Pelucios-MacBook-Pro Arq[96568]: TRACE [thread 1603] 0x1000df520 Process.m:126 Process with CFBundleIdentifier = com.haystacksoftware.ArqAgent is running
Mar 18 12:37:16 Alisson-Pelucios-MacBook-Pro Arq[96568]: TRACE [thread 8c77] 0x102a7b530 BufferedInputStream.m:79 <BufferedInputStream <FDInputStream fd=14 /Users/sellaro/Library/Arq/Cache.noindex/1288h2gepgcjx1gcg482-com-haystacksoftware-arq-sa-east-1/7EA780CA-6643-4ACC-9A4B-798781656161/inprogress/todo.txt> EOF after 0 of 1 bytes received
Mar 18 12:37:16 Alisson-Pelucios-MacBook-Pro Arq[96568]: TRACE [thread 1603] 0x1000df520 Process.m:126 Process with CFBundleIdentifier = com.haystacksoftware.ArqAgent is running
(...)
This repeats up to the moment I re-start Arq Agent.