It’s a little difficult to duplicate this without some example data, but here is what I came up with.
arr = np.array([np.array([1,2,3]), np.array([1,2,3,4])])
arr
array([array([1, 2, 3]), array([1, 2, 3, 4])], dtype=object)
np.savetxt('x.txt', arr)
TypeError: Mismatch between array dtype ('object') and format specifier ('%.18e')
As pointed out by @Artier there is a little snippet at the end of the accepted answer in Write object array to .txt file
that points out you can just save the array as a string with fmt="%s". Using this format seems to solve the problem for me (again I can’t recreate your issue exactly without a sample of data).
np.savetxt('x.txt', arr, fmt="%s")
I would point out that if you are looking to save disparate arrays and want a single location to keep them savez is very useful.