Certificate pinning and Let's Encrypt

as intermediates can change at any time without notice.

updates are posted in that forum:

eg. Beginning Issuance from R3

X4 was an backup intermediate for X3 and never signed any request.
R4 is the new backup for R3

in a few weeks/month E1 will be used for EC certificates with E2 as a backup.

not sure pinning ISRG Root X1, ISRG Root X2 could be better.