Invalid duration format (9.4.5)

[Jarmo Hurri]

Greetings.

To get my work done, I had to switch from master branch to stable, but
now I started getting "invalid duration format" error when trying to
create my daily agenda:

org-duration-to-minutes: Invalid duration format: #("12:45-14:15 +1w" 0 15 
(fontified nil org-category "schedule"))

Here is the corresponding row, and the preceding row, from file
schedule.org:

<2021-04-15 Thu 09:15-10:45 +1w>
<2021-04-19 Mon 12:45-14:15 +1w>

Any hints?

Jarmo