certificate verification failures during pkg bootstrapping on a 15-PRERELEASE PKGBASE installation

i grabbed the latest iso image snapshots of both bootonly and disc1 of 15-PRELEASE (e.g. https://download.freebsd.org/snapshots/ISO-IMAGES/15.0/FreeBSD-15.0-PRERELEASE-amd64-20250819-02a8fadd2c4d-279701-bootonly.iso.xz and https://download.freebsd.org/snapshots/ISO-IMAGES/15.0/FreeBSD-15.0-PRERELEASE-amd64-20250819-02a8fadd2c4d-279701-disc1.iso.xz ) upon doing pkgbase installation using the "packages (experimental)" from the "select installation type" window, pkg bootstrapping and installation falls with

> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> pkg: Error fetching https://pkg.FreeBSD.org/FreeBSD:15:amd64/latest/Latest/pkg.pkg: Authentication error
> A pre-built version of pkg could not be found for your system.
> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> pkg: Error fetching https://pkg.FreeBSD.org/FreeBSD:15:amd64/kmods_latest/Latest/pkg.pkg: Authentication error
> A pre-built version of pkg could not be found for your system.
> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> Certificate verification failed for /C=US/O=Let's Encrypt/CN=E5
> 10A0E522582C0000:error:0A000086:SSL routines:tls_post_process_server_certificate:certificate verify failed:/usr/src/crypto/openssl/ssl/statem/statem_clnt.c:2124:
> pkg: Error fetching https://pkg.FreeBSD.org/FreeBSD:15:amd64/base_latest/Latest/pkg.pkg: Authentication error
> A pre-built version of pkg could not be found for your system.
> Bootstrapping pkg from pkg+https://pkg.FreeBSD.org/FreeBSD:15:amd64/latest, please wait...
> Bootstrapping pkg from pkg+https://pkg.FreeBSD.org/FreeBSD:15:amd64/kmods_latest, please wait...Bootstrapping pkg from pkg+https://pkg.FreeBSD.org/FreeBSD:15:amd64/base_latest, please wait...

curiously bootstrapping pkg on a system created by the "traditional" installation happens without a hitch