openldap 2.4.16 crash

Hi

Slapd process crash every day.
We have activeted debug level at 256. this lets us see this log before the
crash

 conn=2 op=1 SRCH base="dc=domain,dc=com" scope=2 deref=2
filter="(&(memberUid=000678)"
 slapd[13011]: conn=2 op=1 SRCH attr=cn
 slapd[13011]: conn=2 op=1 SRCH attr=cn
 slapd[13011]: conn=2 op=1 SRCH attr=cn
 slapd[13011]: conn=2 op=1 SEARCH RESULT tag=101 err=0 nentries=30 text=
 slapd[13011]: conn=2 op=1 SEARCH RESULT tag=101 err=0 nentries=30 text=
 slapd[13011]: conn=2 op=1 SEARCH RESULT tag=101 err=0 nentries=30 text=
 slapd[13011]: conn=2 fd=16 closed (connection lost)
 slapd[13011]: conn=2 fd=16 closed (connection lost)
 slapd[13011]: conn=2 fd=16 closed (connection lost)

We put th idletimeout to 60 s to close properly idle connexions. But this
does not provide any change.

does anybody have an idea about that ?
how to fix that ?

Thanks a lot