HttpException 423 Resource is Locked when downloading a file with firefox to Nextcloud share

i have an issue with a ~30MB downloaded from a slow website with firefox to a NextCloud 21.0.4 share mounted with RaiDrive 21.5.20 which fail almost everytime. No issue on a local drive of course.
Here is the log (anonymized)

2021-09-02 11:17:29.665 [ERROR] FILESYSTEM : xxx : CreateFile Error : \xxx.zip.part : {“WinErrorCode”:33,“NotifyErrorCode”:107,“RaiException”:"",“Filename”:"/xxx.zip.part",“Processname”:"\Device\HarddiskVolume2\Program Files\Mozilla Firefox\firefox.exe",“WebExceptionStatus”:“ProtocolError”,“InnerException”:“The remote server returned an error: (423) Locked.”,“WebResponseCode”:423,“HttpException”:“423 Resource is Locked”,“HttpReferenceMessage”:"<?xml version=\"1.0\" encoding=\"utf-8\"?>\n<d:error xmlns:d=“DAV:” xmlns:s=“http://sabredav.org/ns”>\n <s:exception>OCA\DAV\Connector\Sabre\Exception\FileLocked</s:exception>\n <s:message>“xxx.zip.part” is locked</s:message>\n</d:error>\n"} : \Device\HarddiskVolume2\Program Files\Mozilla Firefox\firefox.exe

if i save this file on a local drive and copy it when finished it’s fine as well