Please apply the following commit from the upstream repo:

===
commit bf147987003678ae70c2c2ed5275ca4d75842990
Author: Dmitry Torokhov <dtor@chromium.org>
Date: Tue Jul 9 11:51:21 2019 -0700

Bump up PassCmd buffer size to 2KiB

While ordinary passwords are rarely longer than 80 bytes, XOAUTH2 tokens
easily exceed this limit. Let's bump it up to 2K to be really safe.

diff --git a/src/drv_imap.c b/src/drv_imap.c
index 0f72c1a..a4959fb 100644
--- a/src/drv_imap.c
+++ b/src/drv_imap.c
@@ -1875,7 +1875,7 @@ ensure_password( imap_server_conf_t *srvc )
if (cmd) {
FILE *fp;
int ret;
- char buffer[80];
+ char buffer[2048]; // Hopefully more than enough room for XOAUTH2, etc. tokens

if (*cmd == '+') {
flushn();
===

since without this fix XOAUTH2 doesn't work.

Thanks.

Original merge request: https://sourceforge.net/p/isync/isync/merge-requests/4/
Upstream repo: https://sourceforge.net/p/isync/isync/ci/master/tree/