Severe lags or disconnects in transition phase of Hell's Kier (Extreme)

Date & Time: several times, most lately on 2018-10-05, around 17:00 UTC.
Frequency: sporadically
World name: Ultros
Character name: Yur'i Hyuga
Monster name: Suzaku
Class/Level: WAR/70
Party or solo: Party
Steps:
1. Start trial "Hell's Kier (Extreme)".
2. During transition phase (after Eternal Flame, when needing to follow arrows), game will sometimes severely lag (letting you miss several arrows) or, more often, completely disconnect. (The last time, five of our party were disconnected simultaneously.)

(Since this is the third time with connection difficulties during exactly that phase, with the rest of the game running smoothly, I am pretty certain this is not just a connection problem. It actually sounds a lot like this known issue, but that's marked as fixed.)

Connection Specs
- Type of internet connection/provider: ADSL / UPC (Vienna, Austria)

Hello yuri_hyuga_ultros,

Thank you for posting about the issue you are having with severe lags or disconnects in Hell's Kier (Extreme). In order to investigate this further, we need some additional information from you. Please fill out the template below with as much information as possible and post a new thread with the information. Once we receive this information, we will continue to investigate this issue for you. Thanks again for posting.

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Thank you for your patience, and best wishes to you.
FINAL FANTASY XIV Game Master Team