@sgiehl I just took a look at this with your fix applied and it is not fixxed for me.
I confirmed #13113 not fixed in 3.6.0.
URL Sent to Matomo : https://........./display/~EtasseE/Backup+plan+October+2017
In the Matomo UI (Behaviour|Page screens) we have: https://........./display/~EtasseE/Backup plan October 2017
The + (PLUS) chars have been replaced with whitepaces. As a consequence the "Open Segmented Visitor Log" does not show any data. As soon there is one whitepace in the "page URL" on this screen it does not work.
Don't have a fix yet, but found the cause of the error. Actions are stored urlencoded in the log_action table, but the value in the segment when opening the segmented visitor log/transitions modal/etc. is not. This results in Matomo looking for an idaction where the name is, eg,
example.org/with+plus-sign/ instead of
exampleo.org/with%2Bplus-sign/. Somewhere the value is either getting urldecoded or needs to be urlencoded.