Good morning,
I am running JabRef 5.0, release 29/11/2018 and Java 8 update 191 on Windows 10 V.1511. My computer is a I5 3.10Ghz, 8Mo. To my standards it is a big machine, it has been dimensioned to handle .raw image processing and does it pretty well.
My data base is, I believe, large : +/-4Mo, 7000+ records, probably +/-1000 Keywords. It is UTF-8 encoded.
I would like to report three issues :

• every time I open the database, JabRef finds duplicated entry keys, offers to solve them, and does nothing (this worked fine on 3.n versions). I know it does nothing, because if I close the database and open it again, I have the same message.
• If I copy / paste an entry, the pasted one has an encoding problem (accented letters - yes, I am french ! - are replaced by white question marks on black diamonds) in the copy.
• After adding a few new entries, JabRef becomes dead slow when typing in the keywords. I did not toggle off the auto-complete feature, it is probably a mistake. I had an issue like that ages ago and your advice has been to toggle off the feature that counts the number of occurrence of each keyword. I did not find this option on 5.0.

I must admit that I would prefer a feature enabling to copy a keyword from the key word list than a feature that tries to be clever and uses a lot of processing time...

I hope it helps,

Regards,

Hervé