JabRef 5.0-dev--snapshot--2019-02-19--master--1b6c7b5b9
Windows 7 6.1 amd64
Java 1.8.0_201
Steps to reproduce the behavior:

Removing selected items from a group using right click on the group and use "remove selected entries from this group" is not working at all. I had to remove entries with right clicking the entry and using the "remove from group" dialog separately on each entry.
This might be related to the following issues:
https://github.com/JabRef/jabref/issues/3112
https://github.com/JabRef/jabref/issues/2857
(see also: https://github.com/JabRef/jabref/issues/1903)
Can confirm first issue for:
JabRef 5.0-dev--snapshot--2019-02-20--master--3589dc3cb
Windows 10 10.0 amd64
Java 1.8.0_201
The second issue, however, is different for me:
Removing selected items from a group using right click on the group and use "remove selected entries from this group" is not working at all. I had to remove entries with right clicking the entry and using the "remove from group" dialog separately on each entry.
I am able to remove multiple entries from a group by selecting them in the main table, right-clicking on the respective group and using "Remove selected entries from this group". So, I cannot confirm the second issue.
Hi, I was able to reproduce this issue on my system and would like to work on resolving it.
However, I am only able to confirm first issue.
@samiyac the issue #4441 might be related as well (haven't tested it though). I've done some preliminary investigation on that issue, it might be useful.
Thanks to @samiyac this should be fixed in the latest development version. Could you please check the build from http://builds.jabref.org/master/. Thanks! Please remember to make a backup of your library before trying-out this version.
Seems ok. Thanks a lot.
I can confirm that his has been fixed in:
JabRef 5.0-dev--snapshot--2019-03-28--master--a73167933
Windows 10 10.0 amd64
Java 1.8.0_201
Note, however, that for large databases (in my case >16,000 entries) when performing such an action, i. e. either adding an item to a group or removing it, the CPU load shoots up to >80% on a Intel Core i7 Quadcore (incl. Hyperthreading). If you add several entries at once or consecutively to a group, it will take a couple of seconds until the item count is updated properly and the CPU load stays >80% for roughly 1 minute. So for large databases, the current implementation currently poses a performance problem.
I guess, the item count for all groups of the database is recalculated after each modification. Possible solutions to this:
I personally would already be happy with the second solution - which is probably easier to implement - since I do not really care about the number of items in a group, but I do care, whether the items that belong to a group are marked as such in the group panel.
If solution 2 is already present and I failed to find it, apologies for that!
Most helpful comment
Seems ok. Thanks a lot.