When splunk run scheduled job which generate result to summary index, once the result is generated, it will write the result into a temporary directory /opt/splunk/var/spool/splunk with a file suffix stash_new.
(For example, RMD541b14054534417ff_2113273468.stash_new)
Splunk by default will monitor this directory with this stanza.
[batch:///home/daniel/splunk-idx/var/spool/splunk/...stash_new]
sourcetype = stash_new
From your description, as you didn't change the scheduled job, one possibility is the sourcetype = stash_new in props.conf is altered by other stanza.
You can check it by using this btool command.
splunk cmd btool --debug props list stash_new
If the returned result have some configuration from local directory, you may need to check whether that configuration is really for stash_new or not.
One example that may break the summary indexing logic is that you accidentally write the followng into local/props.conf without any stanza. That configure will applied to [stash_new] as well.
cat etc/system/local/props.conf
INDEXED_EXTRACTIONS = CSV
## As above configure is not under any stanza, it will apply to all other stanza. Don't configure like this.
