From log file you provided I see that RSS got increased from 2Gb to 4.5Gb however SHOW INDEX STATUS reports almost same RAM usage. That seems like memory leak.
To make sure what is command line you issue to get ps of searchd ?
Could you provide data that reproduces that case here locally to our write only FTP?
ftp: dev.manticoresearch.com
user: manticorebugs
pass: shithappens
I need query log file with SphinxQL format for time you get that log - from 2018-06-22 16:28:34 to 2018-06-25 10:30:00. Index files along with config and stopwords.txt file.
I’d like to replay queries from query log and check searchd memory consumption then narrow down search to any query that cause that leak.