dbmail/imap4d Alert:[db] db_con_get(+254): Thread is having trouble obtaining a database connection. Try [0]

hello again,

recently upgraded dbmail to version 3.1.17 with opensuse 42.1 and 
mariadb 10.0.22
with libzdb version 3.1

mariadb has the following options in my.cnf

max_connections = 500
wait_timeout = 1800
interactive_timeout = 1800

as far as i can tell all seems to be running fine.

but i discovered some lines in the error log:

2016-03-08T16:55:09.750824+01:00 cx20 dbmail/imap4d[4066]: Alert:[db] 
db_con_get(+254): Thread is having trouble obtaining a database 
connection. Try [0]
2016-03-08T17:00:45.967559+01:00 cx20 dbmail/imap4d[4066]: Alert:[db] 
db_con_get(+254): Thread is having trouble obtaining a database 
connection. Try [0]
2016-03-08T17:00:47.511551+01:00 cx20 dbmail/imap4d[4066]: Alert:[db] 
db_con_get(+254): Thread is having trouble obtaining a database 
connection. Try [0]
2016-03-09T00:33:05.383613+01:00 cx20 dbmail/imap4d[4066]: Alert:[db] 
db_con_get(+254): Thread is having trouble obtaining a database 
connection. Try [0]
2016-03-09T05:15:35.886976+01:00 cx20 dbmail/imap4d[4066]: Alert:[db] 
db_con_get(+254): Thread is having trouble obtaining a database 
connection. Try [0]
2016-03-09T05:16:39.385184+01:00 cx20 dbmail/imap4d[4066]: Alert:[db] 
db_con_get(+254): Thread is having trouble obtaining a database 
connection. Try [0]
2016-03-09T05:30:39.652154+01:00 cx20 dbmail/imap4d[4066]: Alert:[db] 
db_con_get(+254): Thread is having trouble obtaining a database 
connection. Try [0]

is this something i need to worry about?

thanks, greetings & all the best
becki