Cant write to vault located on CIFS-share

No matter if i use webdav or fuse, I cant write even the smallest file to a vault thats being mounted by Nemo in GVFS. This actually used to work.

I get “Input/output error” while writing a file, it shows up as zero-length.

I get the following exception in ryptomator while trying to write a file

18:34:52.918 [Thread-100] ERROR o.c.f.fuse.ReadWriteFileHandler - Flushing file failed.
java.io.IOException: Exceptions occured while writing
	at org.cryptomator.cryptofs.fh.ExceptionsDuringWrite.throwIfPresent(ExceptionsDuringWrite.java:29)
	at org.cryptomator.cryptofs.ch.CleartextFileChannel.forceInternal(CleartextFileChannel.java:214)
	at org.cryptomator.cryptofs.ch.CleartextFileChannel.force(CleartextFileChannel.java:207)
	at org.cryptomator.frontend.fuse.OpenFile.flush(OpenFile.java:102)
	at org.cryptomator.frontend.fuse.ReadWriteFileHandler.flush(ReadWriteFileHandler.java:103)
	at org.cryptomator.frontend.fuse.ReadWriteAdapter.flush(ReadWriteAdapter.java:288)
	at ru.serce.jnrfuse.AbstractFuseFS.lambda$init$6(AbstractFuseFS.java:144)
	at jnr.ffi.provider.jffi.NativeClosureProxy$$impl$$14.invoke(Unknown Source)
	Suppressed: java.io.IOException: Operation not supported
		at java.base/sun.nio.ch.FileDispatcherImpl.pwrite0(Native Method)
		at java.base/sun.nio.ch.FileDispatcherImpl.pwrite(FileDispatcherImpl.java:68)
		at java.base/sun.nio.ch.IOUtil.writeFromNativeBuffer(IOUtil.java:109)
		at java.base/sun.nio.ch.IOUtil.write(IOUtil.java:79)
		at java.base/sun.nio.ch.FileChannelImpl.writeInternal(FileChannelImpl.java:850)
		at java.base/sun.nio.ch.FileChannelImpl.write(FileChannelImpl.java:836)
		at org.cryptomator.cryptofs.fh.ChunkIO.write(ChunkIO.java:51)
		at org.cryptomator.cryptofs.fh.ChunkSaver.save(ChunkSaver.java:35)
		at org.cryptomator.cryptofs.fh.ChunkCache.removeChunk(ChunkCache.java:48)
		at com.google.common.cache.LocalCache.processPendingNotifications(LocalCache.java:1810)
		at com.google.common.cache.LocalCache$Segment.runUnlockedCleanup(LocalCache.java:3463)
		at com.google.common.cache.LocalCache$Segment.postWriteCleanup(LocalCache.java:3439)
		at com.google.common.cache.LocalCache$Segment.clear(LocalCache.java:3216)
		at com.google.common.cache.LocalCache.clear(LocalCache.java:4272)
		at com.google.common.cache.LocalCache$LocalManualCache.invalidateAll(LocalCache.java:4911)
		at org.cryptomator.cryptofs.fh.ChunkCache.invalidateAll(ChunkCache.java:79)
		at org.cryptomator.cryptofs.ch.CleartextFileChannel.forceInternal(CleartextFileChannel.java:213)
		... 6 common frames omitted

Version 1.4.15
Linux Min 19.2