concrete5 Environment Information
# concrete5 Version
Core Version - 5.7.5.9
Version Installed - 5.7.5.9
Database Version - 20160615000000
# concrete5 Packages
Calendar (1.0.1), eCommerce with Snipcart (1.3.3), Neat (0.9.2), Page Redirect (2.0), Page Selector Attribute (2.0), Simple Slider (1.0).
# concrete5 Overrides
blocks/page_list/templates/beer_grid_3_wide/view.php, blocks/page_list/templates/beer_grid_3_wide/view.css, blocks/page_list/templates/beer_grid_3_wide, blocks/page_list/templates, blocks/page_list, blocks/autonav/templates/breadcrumb_nybp.php, blocks/autonav/templates, blocks/autonav, blocks/calendar/controller.php, blocks/calendar, blocks/snipcart_product/view.php, blocks/snipcart_product, languages/cs_CZ/LC_MESSAGES/messages.mo, languages/cs_CZ/LC_MESSAGES, languages/cs_CZ, languages/de_DE/LC_MESSAGES/messages.mo, languages/de_DE/LC_MESSAGES, languages/de_DE, languages/en_GB/LC_MESSAGES/messages.mo, languages/en_GB/LC_MESSAGES, languages/en_GB, languages/fi_FI/LC_MESSAGES/messages.mo, languages/fi_FI/LC_MESSAGES, languages/fi_FI, languages/it_IT/LC_MESSAGES/messages.mo, languages/it_IT/LC_MESSAGES, languages/it_IT, languages/nl_NL/LC_MESSAGES/messages.mo, languages/nl_NL/LC_MESSAGES, languages/nl_NL, languages/ru_RU/LC_MESSAGES/messages.mo, languages/ru_RU/LC_MESSAGES, languages/ru_RU, languages/tr_TR/LC_MESSAGES/messages.mo, languages/tr_TR/LC_MESSAGES, languages/tr_TR, languages/da_DK/LC_MESSAGES/messages.mo, languages/da_DK/LC_MESSAGES, languages/da_DK, languages/el_GR/LC_MESSAGES/messages.mo, languages/el_GR/LC_MESSAGES, languages/el_GR, languages/es_PY/LC_MESSAGES/messages.mo, languages/es_PY/LC_MESSAGES, languages/es_PY, languages/fr_FR/LC_MESSAGES/messages.mo, languages/fr_FR/LC_MESSAGES, languages/fr_FR, languages/ja_JP/LC_MESSAGES/messages.mo, languages/ja_JP/LC_MESSAGES, languages/ja_JP, languages/pt_BR/LC_MESSAGES/messages.mo, languages/pt_BR/LC_MESSAGES, languages/pt_BR, languages/sv_SE/LC_MESSAGES/messages.mo, languages/sv_SE/LC_MESSAGES, languages/sv_SE, views/dialogs/event/form.php, views/dialogs/event/frontend/view.php, views/dialogs/event/frontend, views/dialogs/event, views/dialogs, blocks/page_list/templates/beer_grid_3_wide/view.php, blocks/page_list/templates/beer_grid_3_wide/view.css, blocks/page_list/templates/beer_grid_3_wide, blocks/page_list/templates, blocks/page_list, blocks/autonav/templates/breadcrumb_nybp.php, blocks/autonav/templates, blocks/autonav, blocks/calendar/controller.php, blocks/calendar, blocks/snipcart_product/view.php, blocks/snipcart_product, languages/cs_CZ/LC_MESSAGES/messages.mo, languages/cs_CZ/LC_MESSAGES, languages/cs_CZ, languages/de_DE/LC_MESSAGES/messages.mo, languages/de_DE/LC_MESSAGES, languages/de_DE, languages/en_GB/LC_MESSAGES/messages.mo, languages/en_GB/LC_MESSAGES, languages/en_GB, languages/fi_FI/LC_MESSAGES/messages.mo, languages/fi_FI/LC_MESSAGES, languages/fi_FI, languages/it_IT/LC_MESSAGES/messages.mo, languages/it_IT/LC_MESSAGES, languages/it_IT, languages/nl_NL/LC_MESSAGES/messages.mo, languages/nl_NL/LC_MESSAGES, languages/nl_NL, languages/ru_RU/LC_MESSAGES/messages.mo, languages/ru_RU/LC_MESSAGES, languages/ru_RU, languages/tr_TR/LC_MESSAGES/messages.mo, languages/tr_TR/LC_MESSAGES, languages/tr_TR, languages/da_DK/LC_MESSAGES/messages.mo, languages/da_DK/LC_MESSAGES, languages/da_DK, languages/el_GR/LC_MESSAGES/messages.mo, languages/el_GR/LC_MESSAGES, languages/el_GR, languages/es_PY/LC_MESSAGES/messages.mo, languages/es_PY/LC_MESSAGES, languages/es_PY, languages/fr_FR/LC_MESSAGES/messages.mo, languages/fr_FR/LC_MESSAGES, languages/fr_FR, languages/ja_JP/LC_MESSAGES/messages.mo, languages/ja_JP/LC_MESSAGES, languages/ja_JP, languages/pt_BR/LC_MESSAGES/messages.mo, languages/pt_BR/LC_MESSAGES, languages/pt_BR, languages/sv_SE/LC_MESSAGES/messages.mo, languages/sv_SE/LC_MESSAGES, languages/sv_SE, views/dialogs/event/form.php, views/dialogs/event/frontend/view.php, views/dialogs/event/frontend, views/dialogs/event, views/dialogs
# concrete5 Cache Settings
Block Cache - Off
Overrides Cache - Off
Full Page Caching - Off
Full Page Cache Lifetime - Every 6 hours (default setting).
# Server Software
nginx/i-Content
# Server API
fpm-fcgi
# PHP Version
5.6.30-10+deb.sury.org~xenial+2
# PHP Extensions
calendar, cgi-fcgi, Core, ctype, curl, date, dom, ereg, exif, fileinfo, filter, ftp, gd, gettext, hash, iconv, json, libxml, mbstring, mcrypt, mhash, mysql, mysqli, mysqlnd, openssl, pcre, PDO, pdo_mysql, Phar, posix, readline, Reflection, session, shmop, SimpleXML, sockets, SPL, standard, sysvmsg, sysvsem, sysvshm, tokenizer, wddx, xml, xmlreader, xmlrpc, xmlwriter, xsl, Zend OPcache, zip, zlib.
# PHP Settings
max_execution_time - 120
log_errors_max_len - 1024
max_file_uploads - 20
max_input_nesting_level - 64
max_input_time - 90
max_input_vars - 1000
memory_limit - 64M
post_max_size - 20M
sql.safe_mode - Off
upload_max_filesize - 20M
mysql.max_links - Unlimited
mysql.max_persistent - Unlimited
mysqli.max_links - Unlimited
mysqli.max_persistent - Unlimited
pcre.backtrack_limit - 1000000
pcre.recursion_limit - 100000
session.cache_limiter - <i>no value</i>
session.gc_maxlifetime - 1440
opcache.max_accelerated_files - 2000
opcache.max_file_size - 0
opcache.max_wasted_percentage - 5
I'm not aware of any technical reason why this shouldn't work, a default block should be able to be added as a default.
I've just tested this myself in both a 5.7 and v8 install, with caching on, and was able to successfully do this. I created a new page type, configured it for adding, went to edit the 'output' for the page and added a Snipcart Product block with a name, price and SKU.
Then when I create new pages of that type that block appears as a default (and when I edit the block it gives me the expected warning about it being a default). If I then go back to the Page Template output, I can view the default block again and edit it.
Looking at your Environment details, it looks like you're running a slightly older version of 5.7, there have been a couple of releases of the 5.7 branch since 5.7.5.9 - I'm wondering if you're hitting a broader concrete5 bug to do with defaults. Are you able to achieve the same thing but with a different block type?
The fact that you're going back to edit the page type output and it says it does not exist is quite strange, I've not seen that myself before.