It could be session related. Every time a client enters into a session Coldfusion seems to leave a footprint and may be holding onto a piece of memory, based on your cookie expiration. I am going to guess your server is incrementally eating up memory. One solution is to reduce the clients entering into sessions and the other is the age old CF solution (e.g. add gobs of ram to your server).
Here is some code you can add to quickly reduce the number of lengthy sessions, based upon the needs of your website. I've used this and it helps but won't eliminate memory hungry CF applications completely.
<cfif (
(NOT Len( cgi.http_user_agent )) OR
REFind( "bot\b", cgi.http_user_agent ) OR
Find( "crawl", cgi.http_user_agent ) OR
REFind( "\brss", cgi.http_user_agent ) OR
Find( "feed", cgi.http_user_agent ) OR
Find( "news", cgi.http_user_agent ) OR
Find( "blog", cgi.http_user_agent ) OR
Find( "reader", cgi.http_user_agent ) OR
Find( "syndication", cgi.http_user_agent ) OR
Find( "coldfusion", cgi.http_user_agent ) OR
Find( "slurp", cgi.http_user_agent ) OR
Find( "google", cgi.http_user_agent ) OR
Find( "zyborg", cgi.http_user_agent ) OR
Find( "emonitor", cgi.http_user_agent ) OR
Find( "jeeves", cgi.http_user_agent )
)>
<cfset THIS.name = "myWebsite_06302019">
<cfset THIS.sessionManagement="Yes">
<cfset THIS.sessiontimeout="#createtimespan(0,0,0,5)#">
<!---<cfset THIS.sessioncookie.timeout = "7" >--->
<cfset THIS.sessioncookie.timeout = "-1" >
<cfelse>
<cfset THIS.name = "myWebsite_06302019">
<cfset THIS.sessionManagement="Yes">
<cfset THIS.sessiontimeout="#createtimespan(0,0,180,0)#">
<!---<cfset THIS.sessioncookie.timeout = "7" >--->
<cfset THIS.sessioncookie.timeout = "#createtimespan(0,0,180,0)#" >
</cfif>