I see quite a few of these in your log:
18-6-12 18:55:26.2|Warn|ProcessDownloadDecisions|Couldn't add report to download queue. Teen.Mom.2.S08E24.720p.web.x264-tbs
[v2.0.0.5163] System.Xml.XmlException: Syntax Error after '<!' characters. http://www.newzbin.com/DTD/nzb/nzb-1.1.dtd Line 2, position 4.
at System.Xml.DTDReader.CompileDeclaration () [0x00237] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/DTDReader.cs:331
at System.Xml.DTDReader.ProcessDTDSubset () [0x000cf] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/DTDReader.cs:233
at System.Xml.DTDReader.GenerateDTDObjectModel () [0x0012f] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/DTDReader.cs:166
at Mono.Xml2.XmlTextReader.GenerateDTDObjectModel (System.String name, System.String publicId, System.String systemId, System.String internalSubset, Int32 intSubsetStartLine, Int32 intSubsetStartColumn) [0x000b8] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/XmlTextReader.cs:2441
at Mono.Xml2.XmlTextReader.ReadDoctypeDecl () [0x00116] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/XmlTextReader.cs:2396
at Mono.Xml2.XmlTextReader.ReadDeclaration () [0x00062] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/XmlTextReader.cs:2237
at Mono.Xml2.XmlTextReader.ReadContent () [0x00128] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/XmlTextReader.cs:1277
at Mono.Xml2.XmlTextReader.Read () [0x00141] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/XmlTextReader.cs:572
at System.Xml.XmlTextReader.Read () [0x0006b] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/System.Xml/XmlTextReader2.cs:563
at Mono.Xml.XmlFilterReader.Read () [0x00000] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/Mono.Xml/XmlFilterReader.cs:232
at Mono.Xml.XmlFilterReader.Read () [0x00000] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/Mono.Xml/XmlFilterReader.cs:232
at Mono.Xml.XmlFilterReader.Read () [0x00061] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.XML/Mono.Xml/XmlFilterReader.cs:240
at System.Xml.Linq.XDocument.ReadContent (System.Xml.XmlReader reader, LoadOptions options) [0x00053] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.Xml.Linq/System.Xml.Linq/XDocument.cs:161
at System.Xml.Linq.XDocument.LoadCore (System.Xml.XmlReader reader, LoadOptions options) [0x00006] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.Xml.Linq/System.Xml.Linq/XDocument.cs:147
at System.Xml.Linq.XDocument.Load (System.Xml.XmlReader reader, LoadOptions options) [0x00035] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.Xml.Linq/System.Xml.Linq/XDocument.cs:140
at System.Xml.Linq.XDocument.Load (System.Xml.XmlReader reader) [0x00000] in /private/tmp/source-mono-mac-4.0.0-bug-33585-hotfix/bockbuild-mono-4.0.0-branch/profiles/mono-mac-xamarin/build-root/mono-4.0.4/mcs/class/System.Xml.Linq/System.Xml.Linq/XDocument.cs:132
at NzbDrone.Core.Download.NzbValidationService.Validate (System.String filename, System.Byte[] fileContent) [0x00024] in M:\BuildAgent\work\b69c1fe19bfc2c38\src\NzbDrone.Core\Download\NzbValidationService.cs:22
at NzbDrone.Core.Download.UsenetClientBase`1[NzbDrone.Core.Download.Clients.Sabnzbd.SabnzbdSettings].Download (NzbDrone.Core.Parser.Model.RemoteEpisode remoteEpisode) [0x00151] in M:\BuildAgent\work\b69c1fe19bfc2c38\src\NzbDrone.Core\Download\UsenetClientBase.cs:76
at NzbDrone.Core.Download.DownloadService.DownloadReport (NzbDrone.Core.Parser.Model.RemoteEpisode remoteEpisode) [0x00175] in M:\BuildAgent\work\b69c1fe19bfc2c38\src\NzbDrone.Core\Download\DownloadService.cs:69
at NzbDrone.Core.Download.ProcessDownloadDecisions.ProcessDecisions (System.Collections.Generic.List`1 decisions) [0x000dd] in M:\BuildAgent\work\b69c1fe19bfc2c38\src\NzbDrone.Core\Download\ProcessDownloadDecisions.cs:76
What is your mono version? There have been a few recent reports with people running ancient versions that cause this error. If it’s 3.10 or something, you’ll want to upgrade.
But not to 5.12.0.266 because Cannot add Handmaid's Tale - Skyhook error