Freron MailMate

macOS Big Sur 11.1
Mailmate 1.13.2 (5672)

If I right click any email attachment and select "open with" it freezes with a beachball trying to display the context menu and then mailmate crashes. If I run it from the terminal I see:

$ /Applications/MailMate.app/Contents/MacOS/MailMate 2021-01-23 09:07:43.717 MailMate[67626:1608836] WARNING: tableColumns changed out from under NSTableView! Please use -addTableColumn: and -removeTableColumn:
2021-01-23 09:07:43.717 MailMate[67626:1608836] WARNING: _tableColumns changed out from under NSTableView! Please use -addTableColumn: and -removeTableColumn:
2021-01-23 09:07:43.717 MailMate[67626:1608836] WARNING: _tableColumns changed out from under NSTableView! Please use -addTableColumn: and -removeTableColumn:
2021-01-23 09:07:43.717 MailMate[67626:1608836] WARNING: _tableColumns changed out from under NSTableView! Please use -addTableColumn: and -removeTableColumn:
2021-01-23 09:07:43.717 MailMate[67626:1608836] WARNING: _tableColumns changed out from under NSTableView! Please use -addTableColumn: and -removeTableColumn:
2021-01-23 09:07:43.717 MailMate[67626:1608836] WARNING: _tableColumns changed out from under NSTableView! Please use -addTableColumn: and -removeTableColumn:
2021-01-23 09:08:26.454 MailMate[67626:1608836] -[NSURL length]: unrecognized selector sent to instance 0x7fd8237af8d0
2021-01-23 09:08:26.470 MailMate[67626:1608836] NSExceptionHandler has recorded the following exception:
NSInvalidArgumentException -- -[NSURL length]: unrecognized selector sent to instance 0x7fd8237af8d0
Stack trace: 0x7fff201d63c9 0x7fff20520c85 0x7fff2040607d 0x7fff20405a38 0x7fff21189624 0x7fff21189536 0x1092bfbc8 0x7fff22ef4bdb 0x7fff22e123f2 0x7fff22f4670d 0x7fff22f4652a 0x7fff286804a0 0x7fff2867f879 0x7fff2867f722 0x7fff286d11c7 0x7fff28704869 0x7fff2882bf09 0x7fff287252af 0x7fff2882f136 0x7fff2882b690 0x7fff2882ac7a 0x7fff286fcdb9 0x7fff2310cede 0x7fff22fa8e19 0x7fff2304af7d 0x7fff2304ae09 0x7fff234d2d66 0x7fff23044fbb 0x7fff2317107b 0x7fff22dcaf58 0x7fff22dc93ea 0x1092d588e 0x7fff22dc812a 0x7fff230a036e 0x7fff22c30b2f 0x7fff22c04df2 0x1091bd6c8 0x7fff20347621 0x1
2021-01-23 09:08:26.516 MailMate[67626:1608836] NSExceptionHandler has recorded the following exception:
NSInvalidArgumentException -- -[NSURL length]: unrecognized selector sent to instance 0x7fd8237af8d0
Stack trace: 0x7fff28680778 0x7fff2867f879 0x7fff2867f722 0x7fff286d11c7 0x7fff28704869 0x7fff2882bf09 0x7fff287252af 0x7fff2882f136 0x7fff2882b690 0x7fff2882ac7a 0x7fff286fcdb9 0x7fff2310cede 0x7fff22fa8e19 0x7fff2304af7d 0x7fff2304ae09 0x7fff234d2d66 0x7fff23044fbb 0x7fff2317107b 0x7fff22dcaf58 0x7fff22dc93ea 0x1092d588e 0x7fff22dc812a 0x7fff230a036e 0x7fff22c30b2f 0x7fff22c04df2 0x1091bd6c8 0x7fff20347621 0x1
Assertion failed: (!needsMainQueue() || pthreadmain_np() != 0), function invoke, file /AppleInternal/BuildRoot/Library/Caches/com.apple.xbs/Sources/SkyLight/SkyLight-569.6/SkyLight/Services/PortStreams/CGSDatagramReadStream.cc, line 147.
Abort trap: 6

The "open with" context menu works fine in the finder.