I wrote about this problem twice. I attached video.
And two times you only ask me where am I from. I'm from Russia. You guess that problem is in my internet connection. And that's all that you do.
Look at it
Packets Pings
Host Loss% Snt Last Avg Best Wrst StDev
1. 192.168.11.14 0.0% 28 0.7 1.1 0.6 2.2 0.2
2. 192.168.1.3 0.0% 28 2.0 2.0 1.3 2.5 0.0
3. 10.63.255.254 0.0% 28 2.8 2.7 1.9 4.1 0.3
4. 10.63.8.254 0.0% 27 3.1 2.7 1.8 3.7 0.3
5. 83.242.252.241 0.0% 27 2.7 2.7 2.0 3.5 0.0
6. 83.242.248.37 0.0% 27 4.9 4.9 4.3 6.0 0.2
7. 212.188.40.157 0.0% 27 6.1 5.9 5.1 7.0 0.0
8. pskir-cr01-ae5.63.sam.stream-internet.net 0.0% 27 73.9 76.0 73.3 92.8 4.9
9. psulnsk-cr01-ae3.63.uln.stream-internet.net 0.0% 27 74.5 75.2 73.3 84.2 2.4
10. pspenz-cr01-ae2.73.pen.stream-internet.net 0.0% 27 72.6 77.9 71.7 99.4 8.8
11. pstamb-cr01-ae4.58.tam.stream-internet.net 0.0% 27 74.4 75.4 73.0 91.9 3.8
12. psnmich-cr01-ae5.68.rzn.stream-internet.net 0.0% 27 86.6 78.1 71.6 141.3 17.2
13. m9-cr05-ae6.62.msk.stream-internet.net 0.0% 27 74.7 74.9 73.1 82.5 2.6
14. a197-cr04-be13-77.msk.stream-internet.net 0.0% 27 78.1 76.4 73.7 89.7 2.9
15. oct-cr03-be1-78.spb.stream-internet.net 3.7% 27 75.0 74.3 73.5 75.0 0.0
16. kivi-cr01-ae2.78.hel.stream-internet.net 0.0% 27 73.6 77.4 73.1 97.3 7.3
17. tct-cr02-ae3.231.ams.stream-internet.net 3.7% 27 68.1 72.4 67.1 103.2 10.2
18. tct-cr01-po1-131.ams.stream-internet.net 0.0% 27 72.9 75.2 71.9 102.1 6.5
19. TenGE13-2.br02.ams01.pccwbtn.net 0.0% 27 68.8 87.1 68.4 286.8 53.3
20. 63.218.251.54 0.0% 27 295.6 651.1 295.6 9861. 1840.
21. 27.0.0.129 0.0% 27 312.2 646.6 289.7 9831. 1835.
22. 27.0.0.147 0.0% 27 289.1 655.5 288.1 9790. 1863.
23. ec2-175-41-192-57.ap-northeast-1.compute.amazonaws.c 0.0% 27 290.2 655.2 289.9 9749. 1854.
24. ???
25. ec2-54-249-250-77.ap-northeast-1.compute.amazonaws.c 0.0% 27 295.2 295.9 294.4 300.3 1.6

I think 300 ms is acceptable. Am I right?
It seems that you don't have enough power on amazon or your app is not optimized because slowing starts when I select one or another list or I add a new task (just one task and I see how it's adding up to 5 seconds. Unbelievable!). 10 items in list is not big data, isnt it?
Sorry if I mistake.