keantoken reported in chat this issue and i was able to reproduce it. He said it is happening with nightly builds since February (2019). Could be a side effect of code cleanup made by me and Flow. Although i have found one such file with January 30 date in my profile. This could also be side effect of Smack update
Usually Spark creates two history files per user: user@server and user@server_current. It stores last 10 messages in the latter one to display in the chat window. Whole history is stored in the first one.
Now the second file is created with userserver_current name. It works correctly though and Spark loads messages into chat window from this file. But user could also have older file with the user@server_current name and this file is not loaded. So a few last messages are not shown this way.
It's a minor issue as chatting a lot with a contact should make that file overwrite older messages anyway and file with a new name will be the most actual one.