I'm running the mod on minecraft version 1.19.2, and I'm constantly getting this error:

[15:41:52 ERROR]: Failed to save chunk [109, 21]
java.util.concurrent.CompletionException: java.lang.AbstractMethodError: Method net/mehvahdjukaar/supplementaries/common/block/tiles/SackBlockTile.getViewers()Ljava/util/List; is abstract
at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:315) ~[?:?] {re:mixin}
at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:320) ~[?:?] {re:mixin}
at java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:722) ~[?:?] {}
at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:482) ~[?:?] {}
at net.minecraft.server.level.ChunkMap.m_140353_(ChunkMap.java:471) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:smoothchunk.mixins.json:ChunkMapMixin,pl:mixin:A}
at net.minecraft.server.level.ChunkMap.m_140280_(ChunkMap.java:442) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:smoothchunk.mixins.json:ChunkMapMixin,pl:mixin:A}
at net.minecraft.server.level.ServerChunkCache.m_201698_(ServerChunkCache.java:323) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:smoothchunk.mixins.json:ServerChunkCacheMixin,pl:mixin:APP:mixins.cobblemon-common.json:ServerChunkManagerMixin,pl:mixin:A}
at net.minecraft.server.level.ServerLevel.m_8793_(ServerLevel.java:313) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:ServerLevelMixin,pl:mixin:APP:supplementaries-common.mixins.json:ServerLevelMixin,pl:mixin:APP:corgilib.mixins.json:MixinServerLevel,pl:mixin:APP:mixins.cobblemon-common.json:MinecraftDedicatedServerMixin,pl:mixin:APP:create.mixins.json:accessor.ServerLevelAccessor,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_5703_(MinecraftServer.java:1005) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:A}
at net.minecraft.server.dedicated.DedicatedServer.m_5703_(DedicatedServer.java:327) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:tombstone.mixins.json:DedicatedServerMixin,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_5705_(MinecraftServer.java:944) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_130011_(MinecraftServer.java:791) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_206580_(MinecraftServer.java:278) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:computing_frames,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:MinecraftServerMixin,pl:mixin:APP:structure_gel.mixins.json:MinecraftServerMixin,pl:mixin:A}
at java.lang.Thread.run(Thread.java:833) [?:?] {}
Caused by: java.lang.AbstractMethodError: Method net/mehvahdjukaar/supplementaries/common/block/tiles/SackBlockTile.getViewers()Ljava/util/List; is abstract
at net.mehvahdjukaar.supplementaries.common.block.tiles.SackBlockTile.getViewers(SackBlockTile.java) ~[supplementaries-1.19.2-2.3.17.jar%23241!/:?] {re:classloading}
at net.minecraft.server.level.ServerLevel.m_8712_(ServerLevel.java:904) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:citadel.mixins.json:ServerLevelMixin,pl:mixin:APP:supplementaries-common.mixins.json:ServerLevelMixin,pl:mixin:APP:corgilib.mixins.json:MixinServerLevel,pl:mixin:APP:mixins.cobblemon-common.json:MinecraftDedicatedServerMixin,pl:mixin:APP:create.mixins.json:accessor.ServerLevelAccessor,pl:mixin:A}
at net.minecraft.server.level.ChunkMap.m_202998_(ChunkMap.java:501) ~[server-1.19.2-20220805.130853-srg.jar%23251!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B,pl:mixin:APP:smoothchunk.mixins.json:ChunkMapMixin,pl:mixin:A}
at java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:718) ~[?:?] {}
... 11 more

What a weird error. So not me nor vanilla add that getViewers method. If I did mod wouldn't have compiled with an abstract method like that. It must be some mod doing something weird, likely some coremodding with ASM or maybe mixins. Thing is there's no way to tell which. Try any optimization mod or stuff that alters block entity. This is an issue on their side