SUMMARY
I tried to copy some videos I took with my phone cam (unfortunately I used move) from my android phone (Pocophone F1 MIUI android 10). The videos started to play but then stopped after about a sec. 

I tried with another video to check the checksum of the file copied through Dolphin from the phone and the file on the phone. They were different! 

I tried to copy the same file from the android phone by using send file from kde connect. This time the checksums matched and the file played. 


STEPS TO REPRODUCE
1. Browse to phone in Dolphin
2. select and copy mp4 file taken with phone
3. Try to play the file on ubuntu with vlc
4. Video fails to play (might show the first few seconds)

OBSERVED RESULT
Video is broken and md5 sums do not match the file on the phone. 

EXPECTED RESULT
Video is not broken and md5 sums match on phone and copied file

I uploaded the test files to my server as they are too big to attach. 
http://peterhofmann.me/files/bugkdeconnect/
VID_20200417_194331.mp4 --> original file successfully copied with send file from kdeconnect with matching checksum
VID_20200417_194331_corrupt.mp4 --> file copied via dolphin which is broken after copy


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Ubuntu 19.10 with installed kubuntu-desktop and eaon kubuntu backports ppa
KDEConnect: 1.4.0 ubuntu from kubuntu backports
KDEConnect-Android: 1.14

(available in About System)
Operating System: Kubuntu 19.10
KDE Plasma Version: 5.18.3
KDE Frameworks Version: 5.67.0
Qt Version: 5.12.4
Kernel Version: 5.6.4-050604-generic
OS Type: 64-bit
Processors: 8 × Intel® Core™ i7-8550U CPU @ 1.80GHz
Memory: 15,5 GiB of RAM


ADDITIONAL INFORMATION
I tried already to unpair and repair phone and laptop but it did not solve the issue. 
It might be that this is only related to video files. I tried to copy a picture and this was copied successfully.