Database corruption using fms 18 and mirrorsync

I used mirrorsync and fms17 without any database corruption for a full year (and fms16 for a year too)

Since I upgraded to fms 18 the database got corrupted twice.

Both times there was the sequence of events like this example of yesterday

9:48 PM a user seems to cancel a sync

1. User canceled action (JDBC URL: jdbc:fmp360://mysite/mydb, SSL: false / SQL statement: SELECT _gSync1, lastErrorMessage FROM MirrorSync WHERE -script='MirrorSync (HeliCloud)' AND -script.param=? / SQL params: [doServerAction

One minute later the user retried

1. Error 802: Unable to open file - Check to make sure that the database file is hosted on FileMaker Server

 In the events.log file

1. 2019-10-16 21:48:49.848 -0400 Error 618 mysite Database or temporary file "filewin:/C:/Windows/Temp/FMTEMPFM2932_5.tmp" is damaged and has been closed. (4294967295)
2. 2019-10-16 21:48:49.848 -0400 Error 681 mysite Closing database "mydb" due to damaged temporary file...

 Any idea of a way to fix this ?