Update2:
More exactly the error occur when setting 'string':

diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index 4a3072ee346..8885bd55846 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -3748,7 +3748,8 @@ Supported arguments for GIO_USE_FILE_MONITOR environment variable:
            (intern
 	    (format "G%sFileMonitor" (capitalize (match-string 1 string)))))
           (t (throw 'doesnt-work nil))))
-	(setq string (substring string (match-end 0))))
+	;(setq string (substring string (match-end 0)))
+        )
 
       ;; Delete empty lines.
       (setq string (tramp-compat-string-replace "\n\n" "\n" string)

With this commented line events occur as expected.

-- 
Thierry