Having the exact same problem and I landed here, it's been happening for about a week now. I'm in Germany connecting to Crystal; I have no problems connecting to an EU data center or otherwise with my internet connection. It's specifically EU -> NA FFXIV servers. Tried adjusting DNS settings to no avail. Using a VPN connected to the east coast helps dramatically but it's still not perfect.
Looking at the tracert, it seems like a node in the US is causing the problem; the ping between Europe and the US looks fine. I've been playing on Crystal for 5 years and usually have around 160ms ping; lately it's been closer to 200ms or dropping completely. It's not gone long enough to cause disconnects, but a noticeable stuttering in player movements, skills and combos not proccing, etc. Very very annoying, and I've never faced a latency issue this bad or this long-lasting before.

Tracing route to neolobby08.ffxiv.com [204.2.29.8]
over a maximum of 30 hops:

1 3 ms 3 ms 2 ms speedport.ip [192.168.2.1]
2 8 ms 6 ms 7 ms p3e9bf3cd.dip0.t-ipconnect.de [62.155.243.205]
3 13 ms 13 ms 15 ms f-ed12-i.F.DE.NET.DTAG.DE [217.5.93.106]
4 13 ms 13 ms 13 ms f-ed12-i.F.DE.NET.DTAG.DE [217.5.93.106]
5 16 ms 13 ms 13 ms 80.150.171.10
6 15 ms 13 ms 13 ms ae-3.r21.frnkge13.de.bb.gin.ntt.net [129.250.3.28]
7 * 28 ms * ae-12.r21.parsfr04.fr.bb.gin.ntt.net [129.250.5.27]
8 106 ms 106 ms 108 ms ae-13.r24.asbnva02.us.bb.gin.ntt.net [129.250.6.6]
9 188 ms 189 ms * ae-2.r24.snjsca04.us.bb.gin.ntt.net [129.250.6.237]
10 193 ms 190 ms 209 ms ae-4.a00.scrmca03.us.bb.gin.ntt.net [129.250.7.57]
11 190 ms 197 ms 194 ms xe-0-0-5-0.a00.scrmca03.us.ce.gin.ntt.net [128.241.2.18]
12 165 ms * 190 ms 204.2.29.241
13 194 ms 191 ms 188 ms 204.2.29.8

Trace complete.
Ping statistics for 204.2.29.8:
Packets: Sent = 20, Received = 17, Lost = 3 (15% loss),
Approximate round trip times in milli-seconds:
Minimum = 162ms, Maximum = 220ms, Average = 190ms
Would really like to see this fixed or at least acknowledged before Dawntrail. If not, I can recommend using a VPN for the time being.