I'm first to criticise a device (and usually get flamed for it) but must say I haven't experienced this keyboard lag at all and I am using Samsung's stock keyboard.I'm not a fan of swift key. I think its ugly and their gesture typing is atrocious (when trying to swipe "too" it almost never ever gets it and always gives me "to" instead. At least with the google keyboard it'll suggest to or too for you to pick from on the suggestion bar. Swiftkey just automatically picks "to" for you. Ughhh). Great for thumb taping though.
I don't know guys. You all know I wanted to like this device. The reality is that its not up to snuff. The under the hood lag that affects the keyboard and other things... It's gonna bother me forever.
I'm on google now launcher BTW.
Have you tried clearing the keyboards app cache, and likewise as this is affecting other keyboard apps - try doing something system wide such as change default language from US English to maybe UK English and see if it makes any difference before switching back.
Likewise you could try doing a wipe cache partition in recovery and see if that sorts it.
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So far my biggest issues are
'Fingerprint reader is inconsistent. Will work well for a while initially before getting near useless with a success rate of around 20%
System ram usage remains consistently high and app refreshes happen too much for a device with 3gb ram. Yes they refresh fast, but doesn't help when the refresh drops me out of an app such as Tapatalk back to the tab screen rather than in last post.
Battery life has been meh! Getting an average of 2.5 - 3hrs sot and often significantly less. Basically less battery than the Galaxy Alpha for me. System tells me no app is using significantly high resources.
Those are my woes currently.