[SOLVED] CB antispam visible on one subdomain but not another

Joomla 3.8.5 CB downloaded and installed 2 days ago on each of two subdomains with identical configuration as far as I can tell.
On one site recaptcha show perfectly at registration; on the other it appears very briefly and then is hidden; looking at the page code with mozilla inspector I see that the field is present but the div is styled 'hidden'; editing this in the css panel of Inspector reveals the recaptcha field; the same occurs if I use any of the CBantispam options ( code, math etc). It is set as default in Global configuration and works fine for contact form but not on registration (I have the field set to display on registration and moderator access level set to superuser), I have copied the google keys from the site that works to the site the fails.

reCaptcha keys are domain specific. You need to generate keys for the domain that doesn't work and use those. If you're using Joomla reCaptcha plugin be sure CB AntiSpam captcha mode is set to Joomla or they'll conflict otherwise be sure Joomlas reCaptcha plugin is disabled. Also ensure you're not applying any conditions to the antispam_captcha field with CB Conditional if using CB Conditional.

Thanks, but the two subdomains are both on the same domain and google assures me that the same keys apply to all sub-domains, and the contact form works fine. I have tried setting the mode to joomla, and I already have the Joomla recaptcha disabled. The subdomain where it works has the cbantispam mode set to recaptcha v2 (joomla captcha disabled). I've also tried re-installing the plug-in, all with no effect.
Just tested the plugin legacy settings; the log-in and forgot logn both work, so it's only the registration that 'displays' the recaptcha styled 'hidden' (regardless of whether mode is set to recaptcha or internal). The field is set to show on the registration form.

Please ensure both CB and CB AntiSpam are completely up to date. If issue persists please PM the URL to your registration form and will try to see why it's being hidden, but it sounds like CB Conditional; are you sure you're not conditioning the antispam_captcha field or the tab its on?

Have reviewed your registration form and it's being conditioned. Doesn't look like by CB Conditional, but looks like by CBSubs. Within CBSubs ensure you aren't hiding the captcha field within your plans under the Workflows tab in the "Hides fields at registration" parameter.

Ah, I see; some of the plans have the antispam field selected in the list of fields o hide in the workflow tab of CBSubs; HOWEVER, I cannot de-select it; if I do so apply or save the form and then re-open the pln, it is selected again. I have noticed that this is not the only field with this behaviour; two other plans have the name field selected. I'll look into this further but it seems very strange.