Can you provide a reproducer (i.e. a self-contained .svx file I can process and get this error)?
I tried to make one, but it processes as expected for me:
olly@gemse:~/git/survex$ cat date-comment-parse-bug.svx
*begin foo
*date 1993.07.17 ; trip 1993-161-15 in logbook
1 2 10.00 000 00
*end foo
olly@gemse:~/git/survex$ cavern date-comment-parse-bug.svx
Survex 1.2.42
Copyright © 1990-2018 Olly Betts
Survey has no fixed points. Therefore I’ve fixed foo.1 at (0,0,0)
Removing trailing traverses...
Concatenating traverses...
Simplifying network...
Calculating network...
Calculating traverses...
Calculating trailing traverses...
Calculating statistics...
Survey contains 2 survey stations, joined by 1 leg.
There are 0 loops.
Total length of survey legs = 10.00m ( 10.00m adjusted)
Total plan length of survey legs = 10.00m
Total vertical length of survey legs = 0.00m
Vertical range = 0.00m (from foo.2 at 0.00m to foo.2 at 0.00m)
North-South range = 10.00m (from foo.2 at 10.00m to foo.1 at 0.00m)
East-West range = 0.00m (from foo.2 at 0.00m to foo.2 at 0.00m)
2 1-nodes.
CPU time used 0.00s
The line shown after each error in your output with the location highlighted suggests cavern think that trip 1993-161-15 in logbook is a line by itself in your case, so perhaps you have some odd invisible character in that line of your survex file? cat -vet arrow.svx would help see that.
