I will start this post by stating that I am not very experienced in database administration, please accept my apologies for any unclear explanation you may find below.
We have a replica postgresql hosted on AWS RDS, which stopped replicating last week. The instance was flagged as Storage-full.
However, while looking at the free storage space on CloudWatch, we realized there were still roughly 46Gb available on the 50Gb-allocated instance. We increased the allocated space to 60Gb and everything went back to normal, but we knew the issue would come back and it did.
The main instance on which this one is replicated is auto vacuumed. I think any writes resulting on the main will be written on the replica, so this is probably not a vacuum issue.
I could not find any indication of problem in CloudWatch metrics.
It appears that the logs could be the issue here but I don't know where to look to investigate this option.
I will edit the question with any relevant information you might suggest in the comments. Thanks for your help.