[MC-179608] Server crashing when trying to load a pre-existing world into it

Getting this crash report when trying to load a single player world into it. Furthermore, I doesn't seem to run a pre-existing multiplayer world in 20w16a. Any ideas why? I'm running the server on ubuntu 18.04 with java 1.8.0_242.

Crash message (for the 1.15.2 world - the 20w16a world does crash but doesn't provide a crash report at /opt/minecraft/server/./crash-reports):

---- Minecraft Crash Report ----
// I blame Dinnerbone.
Time: 4/20/20 11:11 PM
Description: Exception in server tick loop
java.lang.RuntimeException: Failed to check session lock, aborting
 at crn.h(SourceFile:95)
 at crn.<init>(SourceFile:51)
 at crp.a(SourceFile:113)
 at crp.a(SourceFile:109)
 at net.minecraft.server.MinecraftServer.a(SourceFile:360)
 at wd.d(SourceFile:219)
 at net.minecraft.server.MinecraftServer.run(SourceFile:628)
 at java.lang.Thread.run(Thread.java:748)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------
-- System Details --
Details:
 Minecraft Version: 1.15.2
 Minecraft Version ID: 1.15.2
 Operating System: Linux (amd64) version 4.15.0-96-generic
 Java Version: 1.8.0_242, Private Build
 Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Private Build
 Memory: 389079584 bytes (371 MB) / 752353280 bytes (717 MB) up to 954728448 bytes (910 MB)
 CPUs: 4
 JVM Flags: 2 total; -Xmx1024M -Xms512M
 Player Count: 0 / 20; []
 Data Packs:
 Is Modded: Unknown (can't tell)
 Type: Dedicated Server (map_server.txt)

So to summarize:

My server can't load a 20w16a pre-existing world, even though the server.jar version is the one mojang is posting in the snapshot page over at minecraft.net
When switching to 1.15.2, this crash report is outputted to /opt/minecraft/server/./crash-reports
When the 20w16a server crash occurs, no crash report is outputted, only this message in /logs/latest.log:

 [13:25:31] [main/ERROR]: Unable to bootstrap registry 'minecraft:chunk_generator_type'
[13:25:31] [main/ERROR]: Registry 'minecraft:chunk_generator_type' was empty after loading
[13:25:31] [main/INFO]: Environment: authHost='https://authserver.mojang.com', accountsHost='https://api.mojang.com', sessionHost='https://sessionserver.mojan...', n$
[13:25:32] [main/FATAL]: Failed to start the minecraft server
java.nio.file.AccessDeniedException: ./world/session.lock
at sun.nio.fs.UnixException.translateToIOException(UnixException.java:84) ~[?:1.8.0_242]
at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:102) ~[?:1.8.0_242]
at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:107) ~[?:1.8.0_242]
at sun.nio.fs.UnixFileSystemProvider.newFileChannel(UnixFileSystemProvider.java:177) ~[?:1.8.0_242]
at java.nio.channels.FileChann...(FileChannel.java:287) ~[?:1.8.0_242]
at java.nio.channels.FileChann...(FileChannel.java:335) ~[?:1.8.0_242]
at act.a(SourceFile:25) ~[server.jar:?]
at cyw$a.<init>(SourceFile:196) ~[server.jar:?]
at cyw.c(SourceFile:185) ~[server.jar:?]
at net.minecraft.server.MinecraftServer.main(SourceFile:940) [server.jar:?]