Messages won't sync between MC and Discord. This is my log with relevant information, i think:

https://hastebin.com/joparipere

[18:55:01 WARN]: [DiscordSRV] [JDA] Attempting to reconnect!

[18:55:01 INFO]: [DiscordSRV] [JDA] Connected to WebSocket

[18:55:02 INFO]: [DiscordSRV] [JDA] Finished Loading!

[18:55:02 INFO]: [DiscordSRV] Found server G:pianmc(172991126297509888)

[18:55:02 INFO]: [DiscordSRV] - TC:eingang(172991126297509888)

[18:55:02 INFO]: [DiscordSRV] - TC:test(315145490247188480)

[18:55:02 INFO]: [DiscordSRV] - TC:minecraftchat(178869562484195328)

[18:55:02 INFO]: [DiscordSRV] - TC:simulatoren(398796865543602176)

[18:55:02 INFO]: [DiscordSRV] - TC:seelsorge(410884800799440896)

[18:55:02 INFO]: [DiscordSRV] - TC:regeln-ingame(467777801987162132)

[18:55:02 INFO]: [DiscordSRV] - TC:tweets(567389039552888856)

[18:55:02 INFO]: [DiscordSRV] - TC:infos-ankündigungen(300676181358018580)

[18:55:02 INFO]: [DiscordSRV] - TC:newsticker(473224091290042368)

[18:55:02 INFO]: [DiscordSRV] - TC:archiv(380451749288214528)

[18:55:02 INFO]: [DiscordSRV] - TC:bilder(294859583418269697)

[18:55:02 INFO]: [DiscordSRV] - TC:schreiben(173724381846044683)

[18:55:02 INFO]: [DiscordSRV] - TC:witze(317025164862685185)

[18:55:02 INFO]: [DiscordSRV] - TC:musik(233181376885686272)

[18:55:02 INFO]: [DiscordSRV] - TC:hgl-films(531532134226067457)

[18:55:02 INFO]: [DiscordSRV] - TC:jugendgarten-diskussionen(537716651815075842)

[18:55:02 INFO]: [DiscordSRV] - TC:videos(188312098361704448)

[18:55:02 INFO]: [DiscordSRV] - TC:irgendetwas-anderes(441647625075294208)

[18:55:02 INFO]: [DiscordSRV] - TC:non-pianmc(486884347832696842)

[18:55:02 INFO]: [DiscordSRV] - TC:support(172991981771816962)

[18:55:02 INFO]: [DiscordSRV] - TC:tribunal(173794725982240771)

[18:55:02 INFO]: [DiscordSRV] - TC:shop-aufträge-bestellungen(464883401963470858)

[18:55:02 INFO]: [DiscordSRV] - TC:ränge-rollen(197728273822777344)

[18:55:02 INFO]: [DiscordSRV] - TC:administratives(366164519031930880)

[18:55:02 INFO]: [DiscordSRV] - TC:administratives-zum-wiki(486901600909131786)

[18:55:02 INFO]: [DiscordSRV] - TC:administratives-zum-forum(498177345644134430)

[18:55:02 INFO]: [DiscordSRV] - TC:administratives-google-sites(567383710911954944)

[18:55:02 INFO]: [DiscordSRV] - TC:anregungen(335158038837329922)

[18:55:02 INFO]: [DiscordSRV] - TC:umfragen(536536008456536074)

[18:55:02 INFO]: [DiscordSRV] - TC:teamchat(179100576469090304)

[18:55:02 INFO]: [DiscordSRV] - TC:team-minecraftchat(566016164354850821)

[18:55:02 INFO]: [DiscordSRV] - TC:console(462281901286096896)

[18:55:02 INFO]: [DiscordSRV] - TC:diskussion-über-das-weitere-fortfahren-von-revival(519168618769022996)

[18:55:02 INFO]: [DiscordSRV] - TC:statistische-zahlen(553583279878569984)

[18:55:02 INFO]: [DiscordSRV] - TC:bewerben(468124954353860628)

[18:55:02 INFO]: [DiscordSRV] - TC:item-erstattungen(468125323591155714)

[18:55:02 INFO]: [DiscordSRV] - TC:protection-antrag(468125265143529473)

[18:55:02 INFO]: [DiscordSRV] - TC:revival(435478201918291979)

[18:55:02 INFO]: [DiscordSRV] - TC:kukkies(531419678917263375)

[18:55:02 INFO]: [DiscordSRV] - TC:ragemode(534474915336683520)

[18:55:02 INFO]: [DiscordSRV] - TC:wahrheit-pflicht(561501978073759754)

[18:55:02 INFO]: [DiscordSRV] - TC:mee6-log(538352458989305856)

[18:55:02 INFO]: [DiscordSRV] - TC:loggerbot(538366608515530762)

[18:55:02 INFO]: [DiscordSRV] - TC:schlafzimmerschlachten(569984805299683396)

[18:55:02 INFO]: [DiscordSRV] - TC:gewaltauseinandersetzungen(569984921347817490)

[18:55:02 INFO]: [DiscordSRV] - TC:redaktion(572880312191811604)

[18:55:02 INFO]: [DiscordSRV] Console forwarding assigned to channel TC:console(462281901286096896)

[18:55:02 WARN]: java.lang.NoClassDefFoundError: github/scarsz/discordsrv/dependencies/google/common/collect/Lists

[18:55:02 WARN]: at github.scarsz.discordsrv.objects.CancellationDetector.(CancellationDetector.java:42)

[18:55:02 WARN]: at github.scarsz.discordsrv.DiscordSRV.init(DiscordSRV.java:397)

[18:55:02 WARN]: at java.lang.Thread.run(Thread.java:748)

[18:55:02 WARN]: Caused by: java.lang.ClassNotFoundException: github.scarsz.discordsrv.dependencies.google.common.collect.Lists

[18:55:02 WARN]: at java.net.URLClassLoader.findClass(URLClassLoader.java:381)

[18:55:02 WARN]: at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:134)

[18:55:02 WARN]: at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:80)

[18:55:02 WARN]: at java.lang.ClassLoader.loadClass(ClassLoader.java:424)

[18:55:02 WARN]: at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

[18:55:02 WARN]: ... 3 more

[18:55:02 ERROR]: [DiscordSRV] DiscordSRV failed to load properly: github/scarsz/discordsrv/dependencies/google/common/collect/Lists. See ERROR/Failed to send debug report: java.io.FileNotFoundException: https://debug.scarsz.me/post for more information.
[Pterodactyl Daemon] Server marked as STOPPING

stop

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It was down because of me doing server migration. It works now.